Goals

• Describe the two-way relationship between water resources and human society
• Explain the distribution and dynamics of water at the surface and in the subsurface of the Earth
• Communicate scientific information in terms that can be understood by the general public
• Interpret graphical representations of scientific data
• Identify strategies and best practices to decrease water stress and increase water quality
• Predict how availability of and demand for water resources is expected to change over the next 50 years

Learning Objectives

In completing this module, you will:

• Analyze the relationship between land use and access to fresh water
• Calculate the population that can be supported by a finite water source
• Evaluate possible solutions to anticipated water shortages
• Evaluate whether access to clean water is a basic human right, or if it should be treated as a commodity
• Distinguish between direct and indirect water use
• Record and analyze your own personal water usage
• Compare your own personal water use habits with those of your peers and others worldwide

Does water have value?

Water is essential to life – both as a basic human need for survival and as an “ingredient” in almost everything we do, from food production to manufacturing to power generation. As we will explore in more detail in Module 2 next week, precipitation, and evaporation – and thus water availability – are unevenly distributed around the globe (Figure 1). This also varies seasonally. Figure 1 shows the average global distribution of precipitation for January; to see an animation over the course of the year, check this out:

Animation showing how the distribution of precipitation changes every month. Blue is heavy precipitation and green is light precipitation.

Credit: Animation 1. MeanMonthlyP" by PZmaps - Own work by uploader, sources: CRU CL 2.0 (New, M., Lister, D., Hulme, M. and Makin, I., 2002: A high-resolution data set of surface climate over global land areas. Climate Research 21: 1–25) and File:Tissot indicatrix world map Mollweide proj.svg by Eric Gaba. Licensed under Creative Commons Attribution-Share Alike 3.0 via Wikimedia Commons

There are obviously some areas of the world that are wetter than others, and these patterns are persistent throughout the year (i.e. the deserts of the American southwest, Northern Africa, and Western Australia are perennially dry; whereas equatorial central America, Africa, and Indonesia are wet). This uneven distribution of water resources lies at the root of many topics we’ll cover in this course, because it is a primary driver of human activity, ranging from population dynamics to types and locations of particular industries, to power generation, to politics. For example, take a look at the maps in Figures 1 and 2. Are there areas of the world that are persistently wetter or drier than others?

Figure 1. Map of global average precipitation in January

Credit: ["MeanMonthlyP" by PZmaps (data sources: M., Lister, D., Hulme, M. and Makin, I., 2002: A high-resolution data set of surface climate over global land areas. Climate Research 21: 1–25; File: Tissot indicatrix world map Mollweide proj.svg by Eric Gaba..) Licensed under Creative Commons Attribution-Share Alike 3.0 via Wikimedia Commons

Figure 2. Availability of freshwater (as of 2000) based on combined river flows and groundwater resources

Click Here for Text alternative of Freshwater Availability picture

The Countries with the least freshwater resources are Egypt (26 meters squared per capita per year) and the United Arab Emirates (61 meters squared per capita per year). The countries with the most freshwater resources are Suriname (479,000 meters squared per capita per year) and Iceland (605,000 meters squared per capita per year). North Africa and the middle east generally have low freshwater resources.

Source: Philippe Rekacewicz, UNEP/GRID-Arendal, World Resources 2000-2001, 'People and Ecosystems: The Fraying Web of Life', World Resources Institute (WRI), Washington, D.C., 2000.

As we’ll see in Module 2, water is transported around the Earth by the hydrologic cycle, in which solar energy drives evaporation of water from the oceans and land surface. This water condenses in the atmosphere to form clouds and eventually to fall as precipitation. Much of that precipitation flows as surface water in rivers and streams. Some of it also infiltrates or percolates into the soil and rock, and becomes groundwater. Surface water constitutes the primary source of water for human activity – it is relatively clean, easy to obtain and move, and constantly replenished (barring prolonged dry periods; as we will discuss in Modules 4 and 8-9). Groundwater constitutes another important source of water for human activity. Although the total volume of groundwater held in fractures and pore spaces in the subsurface is large, it is replenished and flows under natural conditions far more slowly than surface water. Additional energy is required to extract groundwater, because it must be pumped from the subsurface, in some cases hundreds of feet or more. For these reasons, groundwater is generally a secondary source of water, in cases where surface water is not readily available or cannot fully meet demand.

Water use and treatment

Once taken for human use, water generally follows a path described in Figure 3 below. After undergoing treatment and distribution, it is used. In the broadest sense, water is constantly being re-used. Water that is taken from rivers or streams for domestic, industrial, or agricultural use was most likely also used by communities or farms up-stream, and subsequently treated and discharged. Over even longer timescales, the water in streams, lakes, and groundwater is the same water that has ever been on Earth – and those same molecules have undoubtedly cycled through many plants and animals before we were even around!

Depending on the nature of water use, it may be re-captured after treatment (“recycled water”) for re-use. As we will see later in the semester, this re-use of water resources is one strategy to cope with water scarcity. The recycled water, depending on its quality, can be used for irrigation (i.e. for parks or golf courses), or for domestic supply. Once the water leaves the “use” loop, it is treated and discharged, typically into surface water bodies. In some cases, the treated water may be used to recharge aquifers instead, either through induced recharge systems or at a smaller scale via passive filtration through soils – for example in leachfields. The discharged water, after mixing with water in the river, stream (or aquifer), becomes a water source for downstream or down-gradient users.

Figure 3. California’s Water Use Cycle

Click for a text description. This will expand to provide more information.

Water is first diverted, collected, or extracted from a source. It is then transported to water treatment facilities and distributed to end-users. What happens during end-use depends primarily on whether the water is for agricultural or urban use. Wastewater from urban uses is collected, treated, and discharged back to the environment, where it becomes a source for someone else. In general, wastewater from agricultural uses does not get treated (except for holding periods to degrade chemical contaminants) before being discharged directly back to the environment, either as runoff to natural waterways or into groundwater basins. There is a growing trend to recycle some portion of the wastewater stream – recycled water – and redistributing it for non-potable end uses like landscape irrigation or industrial process cooling.

Source: California Energy Commission

Some cities are sited in areas where water is available - or was at the time they were settled - including Las Vegas, Los Angeles, Chicago, St. Louis, and Pittsburgh (Figure 4). In some cases, and as we will discuss in detail in later modules in the course, rapid development and growing demand can outpace the original and limited water source for a city or region, leading to a vicious cycle of water acquisition, growth enabled by water availability, and subsequent water stress.

Figure 4: Night image of the continental U.S. from data acquired by the Suomi NPP satellite in 2012.

Source: NASA Earth Observatory

Figure 5: Annual precipitation for 2013, overlain on the same nighttime image.

Source: NOAA

Many of America’s major manufacturing centers (i.e. the rust belt) are located in areas where major rivers and canals provided a means for transport of raw materials and goods, power generation, water supply for processing and cooling, and conveyance of waste. At small scale, harnessing hydropower was accomplished by mills; at larger scales in modern dams, it is through hydroelectric power generation. Major rivers also provide the water supply for irrigation-based agriculture in some areas, where precipitation is not sufficient or consistent enough to support crops.

Figure 6: Nighttime view of the Nile River Valley and Delta, on Oct. 13, 2012, from the Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi NPP satellite.

Source: NASA Earth Observatory/Suomi NPP

Indeed, for these reasons, rivers in many parts of the world are considered the “lifeblood” of society (Figure 6). For example, the Nile River valley in Egypt comprises ~5% of the land area, yet is home to nearly the entire population of 78 million, with a population density among the highest in the world (more than 1000 people per square km). Despite the obvious connection between water availability and human needs, the story of water resource distribution and population growth is not that simple! In some cases, major engineering projects in which millions of acre-feet of water are moved across states or continents have allowed cities and irrigated agricultural regions to flourish in water-scarce parts of the world. In others, major dams or new water sources (i.e. deep groundwater, reclaimed water, or desalination) have provided a means for cities to prosper in unlikely places. For example, take another look at Figure 4 above. The concentration of nighttime lights provides a reasonable proxy for population density. In many parts of the U.S., they follow the water: along the St. Lawrence, girdling the Great Lakes, and along the Mississippi River. Yet other major population centers have sprung up in perennially dry regions, mainly in the deserts of the southwest: Los Angeles, Las Vegas, Tucson, and Albuquerque.

Learning Checkpoints

1. Inspect Figures 4 and 5 and compare the two maps. Note 3 major cities that are near large water sources (rivers or lakes). View Figures 4 and 5above.

Click for answer.

ANSWER: Answers will vary, but examples include the cities around the Great Lakes (Chicago, Toledo, Milwaukee) as well as along the Mississippi River (St. Louis) and along the East Coast (New York, Philadelphia).

2. List 3 cities or regions of high population density that are not near major water sources, and/or lie in areas of low precipitation.

Click for answer.

ANSWER: Answers will vary, but most examples are in the Southwestern US – in Utah, Colorado, Arizona, California, and Nevada. Prominent examples include Los Angeles, Las Vegas, Salt Lake City, and Phoenix.

3. Do you know anyone who lives in one of these dry areas, or have you thought about moving there?

The distribution of water-rich and water-poor regions is of course not the whole story – access to clean water isn’t just about the amount of water that falls as precipitation. It’s also about the infrastructure needed to obtain, treat, transport, and deliver potable water. And that’s just the water supply. Disposal and sanitation of dirty water are equally important and require a means of transporting waste away from the distributed sources, collecting it and treating it, and discharging it safely. Ideally, both supply and waste conveyance systems should also be monitored for performance and for their impacts on water quality.

In some areas, water is plentiful, but access to clean water is not (Figures 7-8). The converse is also true, mainly in developed nations where water projects, desalination, or dams provide a water supply to regions that receive little precipitation. There is also a clear distinction between access to clean water in rural and urban areas (Figure 7), wherein access in rural areas, even in developed nations, lags behind that in urban areas.

Figure 7: Access to clean water supply and sanitation in urban and rural areas. Note that rural areas lag behind urban ones in access to clean water and sanitary disposal, and developing nations lag behind developed ones.

Click the link to expand for a text description of Figure 7.8

Access to clean water supply and sanitation in urban areas.

Year	Status	Water Supply	Improved Sanitation
1990	World	95%	79%
1990	Developing	92%	61%
2004	World	96%	80%
2004	Developing	91%	70%

Access to clean water supply and sanitation in rural areas.

Year	Status	Water Supply	Improved Sanitation
1990	World	63%	26%
1990	Developing	61%	19%
2004	World	72%	39%
2004	Developing	70%	35%

Source: United Nations Environment Programme Vital Water Graphics

Access to clean water differs between rural and urban areas, and between developed and developing nations. In general, in rural areas, even in developed nations, access to water and sanitation lags behind that in urban areas. Globally, the areas with the poorest access to clean drinking water are in equatorial and sub-Saharan Africa, and parts of South America and southeast Asia (Figure 8).

One might imagine that access to clean water and sanitation would be strongly correlated with water-related illnesses and death. For example, compare the maps in Figures 8 and 9.

Figure 8: Global access to clean water supply by nation.

Source: World Health Organization, WHO

Figure 9: Global access to clean water supply by nation.

Source: World Health Organization, (WHO)

How much water do we use, and for what? Water “permeates” almost every aspect of our lives (no pun intended!). Some uses of water are obvious – for example, municipal and domestic supply used for drinking, cleaning, flushing and watering. Others are less obvious, such as water used for irrigation to grow produce, grains, or feed. The water needed to raise livestock is one step further removed, since the water “used” to produce the product includes the water that must go into growing feed. Yet other uses of water are even less visible, for example for refining fuels, cooling for thermo-electric power generation, and the manufacturing of almost everything in our day-to-day lives.;

Because the types and scales of water use vary widely – from domestic wells that pump at a few gallons per minute, to allocations of major rivers in billions of gallons, the units of measurement used for water management also span an enormous range (see Units).

How much and for what purposes?

Globally, there is a widely varied usage of water, as a result of differing total populations and population densities, geography and climate (i.e. water availability), cultures, economies, lifestyles, and water use and reuse efficiency. This can be described both in terms of total water abstraction from surface water and groundwater sources and as per capita water withdrawal. It can also be divided to consider the end uses (for example, as percentages of the total use), or to consider the source of the water. Each of these facets of water use illuminates different aspects of the “water story”.

In many industrialized nations, the dominant water uses are for industry (including thermoelectric power generation, manufacturing, etc…) and agriculture (Figures 10-11). In contrast, domestic and municipal water use generally constitutes less than 15-30% of the total. In developing nations, this is somewhat different – total water use is smaller, less is used for industry, and the proportion used for domestic water supply is larger.

In the U.S., the average per capita use of domestic or municipal water (i.e. the most direct uses – those that would be measured by the water meter at your home) is about 215 m³ per person per year, equivalent to 156 gallons per day (as of 2002). For comparison, the total abstraction of water from surface and groundwater sources in the U.S. is about 1700 m³/person/yr, or 1230 gallons per day. The difference in these numbers represents the large proportion of water that goes to so-called “indirect” uses: food production, manufacturing, power generation, and mining, among others.

In contrast, in sub-Saharan Africa, total water use is less than 200 m³ per person per year (less than 12% of water use in the U.S.). Total abstractions in Western Europe are about 600 m³ per person per year, about 850 m³ per person per year in the Middle East; and 1150 m³ per person per year in Australia. Among those nations with the highest water use, agriculture accounts for anywhere from <40% of use (U.S.), to 67-81% (India and China), to as much as 96% (Pakistan). Industrial use (including power generation) ranges from over 80% of total water use to less 1%. In the U.S. water use for power generation is near 50%; in China, it constitutes 25% and in India about 5%. Germany, Russia, Canada, France, and much of Western Europe use around 60% of withdrawn water for power generation. Municipal and domestic water use typically constitutes about 10-20% of the total and varies little among the worlds most populous countries (Figure 9). You can explore these patterns on your own via a useful interactive plotting engine at Gapminder.

It is important to note that because many products are imported or exported across state and national borders, the total abstractions of water in a given place do not necessarily map to the distribution of water “consumption” there. Consider tomatoes that are transported from California to Massachusetts. The water withdrawal from rivers and aquifers needed to grow the tomatoes would appear on California’s “water tab”, but the eventual use of that water would be elsewhere. The same goes for agricultural and industrial products exported internationally. This flow of indirectly used water, embedded in products, is termed virtual water, and is defined as the amount of water used in generation of the product, or alternatively, the amount of water that would be needed to generate the product at the site where it is ultimately used. It is “virtual” because the water use is indirect; it is required to make or grow the item but is not actually physically contained in the item or transported with it.

Consumptive vs. Non-consumptive Use

Another important aspect of water use is the degree to which the water is available for recycling and/or reuse (Figure 12; cf. Figure 2). For some water uses, including industrial or domestic applications, the wastewater is captured, treated, and may be reused. These are termed nonconsumptive uses. For example, water used in homes is, for the most part, recaptured for treatment and discharged to surface water or groundwater systems – or for recycling of supply. In this sense, the water is not removed from the system (i.e. not “consumed”). In other applications, the water is effectively removed from the Earth’s surface environment and is not available to be re-captured. These are consumptive uses. Examples include water used for agriculture, which is mostly transpired by plants or evaporated and thus transferred to the atmosphere, or thermoelectric power generation, in which much of the water also evaporates (think of the steam you may have seen rising from power plants – this is consumptive water use, in action!).

Figure 10. Water use in the U.S., shown as five-year averages, from 1950-2015. The graph shows total water withdrawals (blue curve), and the partitioning of those uses between sectors. Click here for a text description

Trends in total water withdrawals by water-use category, 1950-2005. Figure examines 5 different water users: public, rural domestic, irrigation, thermoelectric and other, and total withdrawals. Rural domestic water withdraws have stayed fairly consistent around 10 billion gallons a day. Public supply has slowly increase from 20 billion to 45 billion. Other uses have decrease by about 10 billion to around 35 billion. Irrigation has increased from 1950-1980 but then decreased slightly until 2005 to around 110 billion. Thermoelectric power increased steeply from 1950-1980 and then leveled out around 170 billion. The total withdrawals trend similarly increases from 1950-1980 and then levels out around 400 billion gallons of water withdrawn per day.

Source: J.F. Kenny et al., U.S. Geological Survey Circular 1344 (2009)

Figure 11. Percentages of water used for various purposes in the U.S. in 2005.

Click Here for Text Alternatie for percentages of water image

Percentages of water used for various purposes in the U.S. in 2005

Usage	Percentage
Public supply	11
Domestic	1
Irrigation	31
Livestock	Less than 1
Aquaculture	2
Industrial	4
Mining	1
Thermoelectric power	49

Source: C.A Dieter, et. al., Estimated Use of Water in the United State in 2015, USGS.

Figure 12. Proportions of water withdrawals used for agriculture (top), industry (middle) and domestic use (bottom) in 2000. Click here for a text description

3 world maps. The first examining the percentage of water withdrawn for agriculture in a different nation. Europe and Canada withdrawal less than 16% for agriculture. The middle East, South East Asia, and Africa do the most agriculture with 63-100% of water withdrawals going to agriculture. The second map examines water withdraws for industry. Russia, Canada, and Europe withdraw over 50% of water for industry. Nations in the Southern hemisphere and the Middle East withdraw the less than 16% for industry. The third map examines water withdraws for domestic use. Greenland and Central African nations withdrawal over 45% of their water for this purpose. The United States and East Asia withdraw the least at lower than 15% for domestic purposes.

Source: United Nations Environment Programme Vital Water Graphics

Figure 13. Proportions of water withdrawals used for agriculture, industry, and domestic use from 1900-2000, and projected for 2005. The gap between extracted and consumed water is shown by the gray band in each panel. Click here to expand for a text description of Figure 13

Extraction vs consumption bar graphs for water in agriculture, domestic use and industry from 1900-2025. Extraction bars are always smaller than consumption bars. Agriculture both extracts and consumes the most water followed by domestic use then industry. All three graphs show an increase in consumption and extraction but the separation of between the two bars grows over time. The most dramatic difference appears in domestic use, followed by industry, then agriculture. The difference between consumption and extraction is highlighted with a grey band. Water may be extracted, used, recycled (or returned to rivers or aquifers) and reused several times over. Consumption is the final use of water, after which it can no longer be reused. That extractions have increased at a much faster rate is an indication of how much more intensively we can now exploit water. Only a fraction of water extracted is lost through evaporation.

Source: United Nations Environment Programme Vital Water Graphics

Units of measurement: volumes, fluxes, and concentrations

The uses of water for human activity vary immensely, and as a result, water resource management covers a wide range of temporal and spatial scales. In some cases, the timescales are short and volumes relatively small (i.e. domestic pumping of several gallons per minute, over timescales of minutes or hours). At the other extreme, water allocations for states or municipalities are often considered in the context of average annual flows in the billions of gallons. Because so many different scales of measurement are used to describe water flux or discharge (volumes of water) and flow rates (the velocity of flow), it is important to have some facility with the various units of measurement and get a sense for their relative magnitudes.

As one example, the total fluxes of water through river systems – commonly used to define allocations of water for states or nations - are measured and reported in acre-feet. This is a unit of water volume equal to the amount of water that covers an area of one acre, one foot deep. One acre-foot is equivalent to 325,851 gallons (see summary of unit conversions from the U.S. Geological Survey), and is often considered as the amount of water needed for a family of four for about one year.

As we’ll discuss in Module 3, over shorter timescales, river discharges are reported in units of cubic feet per second (cfs), cubic meters per second (m3/s), or gallons per minute (gpm). As one example, on average, Spring Creek carries about 50 cfs at Houserville, PA; this increases downstream to about 90-100 cfs at Axemann as the creek is fed by springs and small tributaries. Short-lived peak discharge may exceed 500 cfs after storm events. For comparison, the flow of the Mississippi River at St. Louis, MO is typically about 400,000-600,000 cfs; in major floods the discharge is over 1,000,000 cfs. The flow rates of rivers and groundwater, as we will see in Modules 3-4 and 6, are reported as a velocity - units of length per time. These measures represent the velocity of the water itself, or of an object (stick, boat, person, etc…) carried by the river or stream.

Yet other key quantities in hydrology are reported in units of an equivalent depth (or length) per time. For example, rainfall rates are described in units of inches, cm, or mm per hour (for individual storm events) or per year (i.e. annual average precipitation). Evaporation rates are reported in the same way – but of course, represent water transport in the opposite direction (up!). The total volume of water these represent depends on the area over which they occur.

A deeper look: the geographic distribution of water uses

It is also instructive to look in more detail at the distribution of different water uses. For example, in the U.S., industry is concentrated East of the Mississippi, mainly in the “steel belt” (also known as the “rust belt”) and in Texas and Louisiana (primarily related to oil and gas extraction) – and thus water use for industry is as well (Figure 14). It’s worth considering whether this pattern is ultimately rooted in the timing of settlement and westward expansion in the U.S., availability of fuel (i.e. coal), or availability of water sources and rivers as a means of transportation for goods and raw materials. The pattern of water withdrawal for agriculture in the US is even more dramatic (Figure 15). Large agricultural water withdrawals from surface water and groundwater are dominantly West of the Mississippi. This is evident from a state-by-state map view and shown even more clearly when plotted simply from West to East (Figure 15, bottom panel).

Figure 14. Total water withdrawals for industrial uses shown by state in map view (top), and arranged from West to East (bottom).

Click link to expand for a text description of Figure 14

Water Withdraws million gal/day by State **approximate numbers

State	Water Withdraws million gal/day
Hawaii	100
Alaska	100
Oregon	250
Washington	500
California	200
Nevada	100
Idaho	100
Arizona	100
Utah	250
Montana	100
Wyoming	100
New Mexico	100
Colorado	200
North Dakota	100
South Dakota	100
Nebraska	100
Texas	2200
Kansas	100
Oklahoma	100
Minnesota	200
Iowa	300
Missouri	100
Louisiana	3200
Arkansas	250
Wisconsin	500
Mississippi	300
Illinois	400
Alabama	500
Tennessee	800
Indiana	2400
Kentucky	250
Michigan	700
Georgia	600
Ohio	650
Florida	250
South Carolina	300
West Virginia	1100
North Carolina	300
Virginia	500
Pennsylvania	900
Maryland	250
D.C.	100
New York	300
Delaware	100
New Jersey	100
Connecticut	200
Vermont	100
Massachusetts	200
Rhode Island	100
New Hampshire	100
Maine	250
Puerto Rico/US Virgin Islands	100

Source: J.F. Kenny et al., U.S. Geological Survey Circular 1344 (2009).

Figure 15. Total 2015 water withdrawals for agricultural (irrigation) uses shown by state in map view (top), and arranged from West to East (bottom).

Click link to expand for a text description of Figure 15

Total Water Withdraws for Agriculture **approximate numbers

State	Water Withdraws million gal/day
Hawaii	200
Alaska	200
Oregon	6000
Washington	3000
California	24000
Nevada	1500
Idaho	16000
Arizona	5000
Utah	4000
Montana	10000
Wyoming	4000
New Mexico	2000
Colorado	13000
North Dakota	200
South Dakota	200
Nebraska	9000
Texas	8500
Kansas	2000
Oklahoma	500
Minnesota	300
Iowa	200
Missouri	1500
Louisiana	900
Arkansas	9000
Wisconsin	300
Mississippi	2000
Illinois	500
Alabama	200
Tennessee	200
Indiana	200
Kentucky	200
Michigan	300
Georgia	750
Ohio	200
Florida	3500
South Carolina	200
West Virginia	200
North Carolina	200
Virginia	200
Pennsylvania	200
Maryland	200
D.C.	200
New York	200
Delaware	200
New Jersey	200
Connecticut	200
Vermont	200
Massachusetts	200
Rhode Island	200
New Hampshire	200
Maine	200
Puerto Rico/US Virgin Islands	200

Source: J.F. Kenny et al., U.S. Geological Survey Circular 1344 (2009).

The source of the water we use also provides clues about where water may be most readily available, and/or where typical rainfall and snowmelt cannot meet demand. Inspect the maps below (Figure 16). Surface water withdrawals are spread more or less uniformly across the U.S., and reflect overall water use reasonably closely. This is influenced in large part by total population, energy production, and industrial and agricultural activity (i.e. CA, TX, NY, and FL are the most populous states). However, groundwater withdrawals (obtained by pumping at wells) are a good indication that surface water flows alone are not sufficient to meet demand.

Figure 16. Total surface water abstractions (left) and groundwater abstractions (right) by state. The color scale is the same as for Figure 15.

Click the link to expand for a text description of Figure 16

Surface Water Withdraws

Amount (million gals./day)	States (random order)
1500-3200	CA
600-1500	ID, TX, CO, IL, MI, OH, NY, NC, VA, TN,
300-600	OR, MO, WI, IN, PA, NJ, DE, SC, AL, LA, AK
300	All others

Ground Water Withdraws

Amount (million gals./day)	States (random order)
1500-3200	n/a
600-1500	CA
300-600	TX, NE, AK
<300	All others

Source: J.F. Kenny et al., U.S. Geological Survey Circular 1344 (2009).

As shown in the Freshwater Resources section, water demand varies by culture and country, while water availability is dependent on climate and geography (see also Module 2). Some areas of the world are already experiencing freshwater shortages and/or their water supplies are unsanitary as the result of improper treatment of waste and inadequate infrastructure to transport and store potable water. The combined specters of climate change and rapid population growth create uncertainty in planning future water supplies.

What will the future bring?

What will the future bring? Good question, right? How can we gauge what water demand and availability will be in the future, particularly with projected large increases in population and potential climate change superimposed? Not to alarm you, but to inform you, we will go through the exercise of making such projections, both for the U.S. and, on a more limited basis, for the world. What do we need to know for making such estimates? First, let's jot down some ideas. Then we will continue the process below.

First, here is an expert opinion as to how the future will go…

In Human Population and the Environmental Crisis Ben Zuckerman and David Jefferson write: “At a low population density, a society may be able to derive its water from rivers, natural lakes, or from the sustainable use of groundwater. As the population grows, so does the volume of water needed (we will assume demand is proportional to population size). Moreover, levels of waste discharge into the environment will grow as the population rises. Thus, the available unmanaged supplies deteriorate at the same time that demand on them is increasing…A destructive synergy is at work: population size affects the water resource in a manner that is not one of simple proportionality.”

What was it Yogi Berra (N.Y. Yankees catcher and later Manager) infamously said…"It's tough to make predictions, especially about the future." Well, that is a truism, but let's see what projections are being made regarding future population growth, because, clearly, that's one of the inputs we need to determine potential future water use globally.The present global population (as of 2024) is approximately 8.05 billion people. Interestingly, the top three countries, in terms of population, are China, India, and, yes, the United States, in that order (Figure 17). But, by 2050 the global population is estimated to be 9.7 billion people by the United Nations—a staggering 20% increase in the next, say, 26 years! So, at the minimum, if we assume that water use will increase linearly on a per person basis, we would expect that this rate of growth will require 20% more fresh water by 2050. Is that a problem? Do we have excess capacity to supply this water?

Do we have excess capacity to supply this water? That is an important question, but you have probably already determined that the real issue is where the population growth occurs and what water resources are available there. The major growth is projected to occur in developing countries (Figure 17). African nations are likely regions for greater than average growth. Interestingly, much of Africa is estimated to have significant groundwater resources (BGS, 2013) that could be developed if necessary. In fact, Nigeria is projected to surpass the population of the U.S. by 2050 (Figures 17-19). One must examine the population density and rate of projected growth vs. water needs. In addition, climate change impacts must be considered.

Figure 17. The distribution of population by country scaled by China (largest red dot) at 1.36 billion people in 2010. (World plot)

Source: Gapminder

Figure 18. Top 10 countries by population from 1950 to 2050, according to UN data.br>

Click link to expand for a text description of Figure 18

1950- total population 2.5 bn

1. China- .5 billion
2. India
3. United States
4. Russia
5. Japan
6. Indonesia
7. Germany
8. Brazil
9. Britain
10. Italy

2013- total population 7.2 bn

1. China-4 bn
2. India
3. United States
4. Indonesia
5. Brazil
6. Pakistan
7. Nigeria
8. Bangladesh
9. Russia
10. Japan

2050 forecast- total population 9.6 bn

1. India-7 bn
2. China
3. Nigeria
4. United States
5. Indonesia
6. Pakistan
7. Brazil
8. Bangladesh
9. Ethiopia
10. Philippines

Source: United Nations

Figure 19. Fertility index (children per woman) by country as a function of per capita income for 2012. Note the higher fertility for African countries. China and the U.S. are well below 2 children per woman.

Click the link to expand for a text description of Figure 19

Chart with GDP/Capita on the X-axis (low to high) and Children per woman (total fertility) on the y-axis for 2012. Different colors and dot sizes are used to represent different countries. The line of best fit would look like a negative exponential function. General trends include high fertility in African countries followed by India, (2-8 children). China, the Americas, and Russia are well below 2 children per woman.

Source: Gapminder

We would probably be better off examining the impacts of climate change on water availability that would increase "water stress," then compare these stresses with those caused by increasing demand, either by population growth in a given region (personal or agricultural demands) or increased water usage resulting from new demands (e.g., energy production) (Figure 20). A number of studies have predicted water supply vs. water demand relationships resulting from climate change. A study by MIT (Massachusetts Institute of Technology) researchers (Schlosser et al., 2014) compared the potential impacts of climate change, on the basis of projected greenhouse gas emission increases in a complex Earth-system model, on water stress in 282 assessment regions (large or multiple watersheds) globally, holding demand constant, to the potential impacts of population growth in the same regions.

Figure 20. United Nations World Population Prospects showing past and projected human population growth, broken down by world region.

United Nations, Department of Economics and Social Affairs, World Population Prospects 2022.

Figure 21. Some estimates of total population growth (UN assessment) from 2010 to 2050. Not all countries experience growth, but note Nigeria and Kenya as examples of increasing population in Africa.

Click link to expand for a text description of Figure 20

Population % change by country

Country	Increase/Decrease	Percent
US	Increase	28
Mexico	Increase	32
Brazil	Increase	18
Germany	Decrease	13
Nigeria	Increase	176
Kenya	Increase	138
India	Increase	34
China	Increase	2
Japan	Decrease	15
Russia	Decrease	16

Source: United Nations, Department of Economics and Social Affairs, World Population Prospects: 2012 Revision, June 2013.

They found that, in most regions, projected population growth with increased demand to 2050 was the greater stressor. These researchers use a Water Stress Index (WSI) defined as WSI = TWR/RUN+INF (TWR is total water required for a given watershed region, i.e. all consumptive uses, RUN is available runoff within the watershed, and INF is inflow to the watershed from adjacent regions. The cutoffs used for interpreting water stress are: WSI<0.3 is slightly exploited, 0.3≤WSI<0.6 moderately exploited, 0.6≤WSI<1 heavily exploited, 1≤WSI<2 overly exploited, and WSI≥2 extremely exploited as originally set out by Smakhtin et al. (2005).

It appears that a substantial proportion of Africa, all of the middle East, India, and central Asia will see increased water stress in the next few decades, largely due to projected population increases. Even the southwestern U.S. is projected to experience expansion and intensification of water stress, but, in this case, mostly as the result of climate change and longer-term drought. Interestingly, the major central U.S. groundwater source, the Ogallala Aquifer, does not appear to be a candidate for significant stress except at its southern end in Texas. However, other studies (see Module 7) suggest that depletion of this aquifer will be more severe.

There are a number of possible methods to enhance supplies of fresh water, each of which has an economic, political, and/or environmental impact.

Some of these strategies have been alluded to previously (e.g., encouraging transfers from agricultural use to drinking water supplies). Water storage behind dams is an old strategy and problematic in a number of ways (see Module 6), including high costs, environmental impacts, and political issues that arise when major rivers flow through multiple countries. Nonetheless, there is still major proposed and ongoing dam building in China and other countries.

Groundwater banking is a newer strategy that requires replenishment of aquifers with treated wastewater and/or with runoff available during times of excess. Costs are associated with treating, impounding, and injecting the water (see Module 7). This will mainly benefit regions with significant groundwater resources.

Recycling and reuse are gaining support with successful projects in the U.S. and elsewhere. Penn State University recycles and reinjects nearly 98% of its treated wastewater and has done so since the 1960s. Orange County, CA, has another successful system (see Module 8). Such systems must overcome consumer opposition, however, because of the perception that consumers will be drinking, well, toilet water! Nonetheless, the water quality in such systems is as good or better than that in municipalities that draw water from rivers downstream from other municipalities that discharge treated wastewater into the same river. Another form of reuse is to employ "gray" water (only partially treated) for irrigation of golf courses in arid to semiarid, water-stressed regions. Las Vegas, NV, has implemented such a system, coupled with the removal of water-hungry turf, for which the economics work and conservation is encouraged.

Desalination may be a last resort because of the costs of energy required to remove salts from seawater or water pumped from saline aquifers in non-coastal regions. However, in water-poor but hydrocarbon-rich middle-Eastern countries the economics may support the desalination of seawater. Alternative energy sources (e.g., solar) or emerging processes such as chemical reverse osmosis may be economical in the future as they become more efficient and less costly. And, of course, if water is deemed to have significant value in the future, the high costs may be more acceptable.

Finally, there are still proposals to import or export water from regions replete with fresh water resources (e.g. Alaska) to severely water-stressed regions (e.g. India). However, the costs of transporting such a commodity across the oceans would appear to exceed the value of that water at its terminus.

All of these strategies will be explored in later modules in more detail.

“Water drop 001”

Source: José Manuel Suárez - Flickr. Licensed under Creative Commons Attribution 2.0 via Wikimedia Commons

Does water have value? If so, how do we set a price for it? And, if we agree that individual access to fresh water is a basic human right or expectation globally (is this generally agreed?), how do we treat water as a commodity? Do we really pay what water is worth?

You are likely all too familiar with bottled water—that convenient liter-sized plastic bottle containing some sort of water, commonly tap water, or filtered spring water, sometimes treated…it appears that, in the U.S., we pay for the convenience of "grab-and-go." For that convenience, we typically pay about $4/gallon, more than we presently pay for a gallon of gasoline! In most municipalities; however, the cost of water delivered in pipes to taps in homes costs far less ($0.003-0.006/gallon). survey by CircleofBlue.org for 2019 water pricing in 30 cities across the U.S. found an average increase of 3.2% in monthly bills for a family of four using an average of 100 gals/day each (12,000 gals/mo or 45.4 m3/mo) from 2018 to 2019, costing an average of $72.93 a month.

Monthly rates for some representative municipalities are shown in the table below, based on data in the CircleofBlue.org 2014 survey and information from water authority websites for some municipalities not covered in that survey (Pittsburgh, PA and State College, PA).Note the large range in rates that do not seem to make sense geographically. For example, arid Phoenix, AZ has the lowest rate, with Las Vegas, NV not far behind, whereas high precipitation, seemingly water-rich regions such as Seattle, WA and Atlanta, GA top the rate list. Note that Los Angeles, CA, Phoenix, AZ, and Las Vegas, NV all depend on Colorado River water, although Los Angeles also draws on northern California sources and all require significant transport infrastructure. So, in part, this disparity in rates results from the costs of maintaining infrastructure and the numbers of households served, as well as the local abundance of water.

Chicago, IL, for example, has nearby Lake Michigan as a source and a large number of users and its rates are relatively low. Little State College, PA has a significant, sustainable groundwater resource (see Module 6), even though the user base is relatively small. Many municipalities have higher rates because they are financing necessary improvements in infrastructure, which can be quite costly.

Municipalities have adopted different methods for scaling water prices. Some, such as Philadelphia and Detroit, provide cost reductions for larger users (decreasing block), some, including New York, have uniform pricing, whereas others, such as Las Vegas and Atlanta, have implemented tiered pricing (block increases) that encourage conservation while trying to maintain the user base. The objective of all municipalities is to sustain income and provide for future infrastructure requirements.

Internationally, pricing varies even more than in the U.S. Figure 22 illustrates average water prices (Kariuki and Schwartz, 2005) and the impact of non-public water suppliers on the cost to the consumer. Where public utilities are not available, the cost to the consumer can be a factor of 10 higher. In part, this occurs because of increases in cost to the water supplier to purchase water from a public or private supplier because of the large volumes purchased with prevailing block pricing increases. Figure 23 shows the step increases for several African and Indian cities. Recall that the average family of four in the U.S. would use about 45 m3/month, but average usage is probably much lower in many developing nations with lower standards of living. Step increases in block pricing appear to be a fair method of pricing to allow low cost for low-volume users and encouraging conservation by imposing higher costs for larger-volume users.

Figure 22. Data for 2005 based on a survey of 47 countries and 93 locations (Kariuki and Schwartz, 2005).

Source: Circle of Blue

Figure 23. Variations in block pricing in several large cities in Africa and India.v($U.S./m3).

Click the link to expand for a text description of Figure 23

Block water tariffs increase in a step-like fashion as water usage (cubic meters/month) increases. For example, take Dakar. From 0-20 cubic meters, there is a \$0.35 tariff but from 20-40 cubic meters there is a \$1.05 tariff and from 40-110 cubic meters it costs \$1.20. Another example is Nairobi. From 0-10 cubic meters, there is a \$0.15 tariff but from 10-30 cubic meters, there is a \$0.25 tariff. From 30-60 cubic meters, there is a \$0.38 tariff and from 60-110 it costs \$0.48

Source: Circle of Blue

Considerations of water pricing are complicated because of the multitude of factors that must be taken into account. These include availability and dependability of water supply locally, state of the distribution infrastructure, and the distribution and size of the user base. Dependability is related to climate impacts, such as prolonged droughts that deplete water reserves. A recent study (Watergy Nexus: The Complex Relationship and Looming Crisis Between Our Thirst For Water and Our Hunger for Energy) highlights an additional factor—the amount and cost of energy to acquire, transport, and treat water. This study argues that the cost of energy (usually electricity, but including fuel if the water is trucked in) must be considered in pricing water. The study uses data for 2013, a year of severe drought in much of the western and central U.S. to show how water prices should be adjusted to guarantee supply and cover costs of acquisition. Although the U.S. Geological Survey indicates that the average energy required to provide 1000 gallons (1 kgal) of water is 1.9kWh of electricity, water-stressed regions such as northern California (3.5 kWh/kgal) and highly stressed southern California (11.1 kWh/kgal) require far more (Figure 24). However, the study suggests that municipalities are not taking this factor into consideration in providing a durable and resilient water supply. During times of water stress, municipalities may have trouble meeting costs, and begin to examine other strategies, such as privatization. Of course, when water availability becomes restricted, costs can go up as in California with severe drought conditions (e.g., see the news article In dry California, water fetching record prices about California water pricing: ).

Figure 24. Variations in water price and examples where water is overpriced or underpriced in consideration of transport costs.

Click for a text description

Drought Map of the Us examining water prices in comparison to source energy per kgal of water to determine over/underpricing. The figure shows that the driest areas of the country are from the Mississippi River westward. The east is also dry but not considered in a drought except for Georgia and South Carolina. On top of the drought map, are several cities with a white ring indicating the price and a black dot indicating energy for every kgal of water. When the price ring is much larger than the black dot then the water is overpriced like in Burlington Vermont. When the energy dot is much greater than the price ring the water is underpriced. The Southwest and up the California coast are either well matched or underpriced. The Midwest is generally fair pricing and the east is generally overpriced.

Source: EnergyPoints

Cash-strapped municipalities with failing water systems might be tempted to contract with private companies to manage their water and sewer systems. Economic drivers, such as the collapse that occurred in 2008, affect users ability to pay for public water systems. In the U.S., about 20% of water supplies are privatized at present. In evaluating this option, one must keep in mind that corporations are for-profit entities, and will need to recoup the full costs of providing water while adding a margin for profit to benefit the corporation and/or their stockholders. Public utilities can be held responsible for controlling costs and providing clean water supplies, whereas it is more difficult for the public to do so for private companies.

Percent of population using privatized water resources as of 2017.

EPA Safe Drinking Water Information System (SDWIS)

There are a number of examples where privatization has apparently failed consumers. Pushed by the costs of renovating their failing water supply infrastructure, Atlanta, GA, for example, handed over control of their water system to United Water, which took over in 1999, with a 20-year contract. Atlanta had long-deferred most maintenance because their revenue was insufficient to cover the full cost of providing service, and because of rapid population growth and their aging system, expansion and improvement were required. Their sewage system was more of a problem than the water supply system, and they were being sued under the U.S. Clean Water Act for that problem as well.

But, in 2003, the city of Atlanta withdrew from the agreement because a number of issues with United Water (see What Can We Learn From Atlanta's Water Privatization for the full story), which included costs, viewed as excessive, and poor performance in maintenance, meter installation, and bill collection.

The situation in Detroit has been much in the news of late (for example – see this MSNBC article, Detroit residents and national allies protest water shutoffs). As a result of the economic downturn, the Detroit Water and Sewer Department has recently gone on a campaign to force users to pay their outstanding water bills with the threat of cutoffs. In addition, the city of Detroit is pursuing the possibility of privatizing its water and sewer systems. Although clearly having its own perspective and position, an interesting argument against water privatization in Detroit is found on The Blue Planet Project website. One common argument against privatization is the rapid increase in the costs of water to consumers. Of course, in many cases, this may occur because the public purveyor was not charging for the full cost of providing the water in the first place.

Michigan lawmakers propose that water bills are capped at 3% of households income and $2 added to bills that can afford to make up for lost income. Claiming that shutting off water is a human rights violation. Read more here.

A 2022 Cornell Chronical story explains that private ownership had the largest impact on annual water bills, which averaged $144 higher in privately owned systems than in public sector systems. Low-income households served by private operators spent 4.4% of their income on water service, about 1.5 percentage points more than in communities with public ownership.