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
• Synthesize data and information from multiple reliable sources
• Interpret graphical representations of scientific data
• Identify strategies and best practices to decrease water stress and increase water quality
• Thoughtfully evaluate information and policy statements regarding water resources
• Communicate scientific information in terms that can be understood by the general public

Learning Objectives

In completing this module, you will:

• Calculate the concentration of contaminant in a reservoir
• Apply government drinking water regulatory standards to identify contaminant levels that might be harmful to human health
• Analyze concentration vs. time data for various dissolved components of river water and ground water
• Infer the processes responsible for seasonal trends in compounds of natural and human origin
• Propose and evaluate methods for mitigating human impacts on water quality
• Evaluate the tradeoff between agricultural productivity and water quality as a result of fertilizer usage and runoff

Elements and molecules have solubilities (the amount that can be dissolved in water before the water is saturated with that element and no more can be held in solution) that depend on their individual properties and styles of bonding to other elements. For example, common table salt (NaCl), when added to water, will dissociate into individual charged ions of Na+ and Cl-. These are held apart from one another "in solution" because they are surrounded and isolated by polar water molecules (Unique Properties of Water section).

Distilled water or "pure" water typically has near-zero concentrations of other components. If concentrations of dissolved elements or compounds are present, they are usually expressed in terms of mass (weight) of the component/unit volume of water, mass element/mass water, or moles element/mass or volume of water.

Typically, the volume of water referenced is a liter (1000 grams--1 kg by mass), and the elemental or component mass is in grams (or milligrams, mg). Milligrams/Liter (mg/L; 0.001g/1000g) or milligrams/kg (mg/kg) is the same as parts per million (ppm) as concentration. You will often see a concentration of a dissolved species in water expressed in either mg/L or ppm.

Molar concentrations, commonly used by chemists, are expressed as a decimal fraction of the mass of Avogadro's Number (a mole) of atoms (6.022 x 10²³) of a given element or elements in a compound, equivalent to atomic or molecular mass. For example, a mole of carbon (¹²C) has a mass of 12 grams, and a mole of carbon dioxide (CO₂) has a mass of 44 grams (¹²C, ¹⁶O, ¹⁶O). So, if a liter water sample contains 0.044g of carbon dioxide (44 ppm), the carbon dioxide concentration would be 0.01 mole/kg.

Who Regulates Drinking Water Quality in the U.S.?

Public drinking water quality is regulated by the U.S. Environmental Protection Agency (EPA) by provisions of the Safe Drinking Water Act (SDWA), although individual states can apply and enforce their own standards if more stringent than those set by the EPA. The SDWA was originally passed by the U.S. Congress in 1974, and has been amended twice (1986, 1996) and now provides standards for drinking-water sources, treatment, and quality at the tap, as well as the disposal of wastewater underground. Private wells pumping groundwater that serve fewer than 25 people are not regulated. They should be tested regularly, however.

It is estimated that there are over 160,000 public drinking-water systems that fall under the aegis of the EPA standards. These standards are health-based and attempt to establish maximum levels (MCL—Maximum Contaminant Level) for possible contaminants that are below those that are thought to cause health problems (you can see specific contaminants and MCLs at EPA: Drinking Water Contaminants - Standards and Regulations). Of course, there are many contaminants for which there are insufficient data to establish stringent limits.

Over the past decade, bottled water, usually sealed in "plastic" containers has become quite popular worldwide. Accoring to bottledwater.org, in the U.S., over 15.9 billion gallons of bottled water were sold in 2022, revenues were more than $46 billion, assuming an average price of $1 per liter. Although convenience is certainly a factor, the perception has been that such water must be safe to drink—perhaps more safe than tap water—also drives bottled water sales. In the U.S., bottled water is actually regulated by the U.S. Food and Drug Administration (FDA), not the EPA. The FDA regulates bottled water as a food (requiring compliance with the Federal Food, Drug and Cosmetic Act) and does not require certified lab testing or violation reporting, even though the FDA does inspect bottling plants and ensures that suitable source waters are used. The FDA also has generally adopted limits for contaminants established by the EPA. Nonetheless, the FDA does not require bottled water companies to disclose to consumers the source of the water, treatment processes, or contaminants it contains, whereas the EPA requires public water systems to report results of their testing annually.

Natural waters have a broad range of total dissolved solids (TDS). Some fresh mountain streams might have TDS concentrations less than 250mg/kg. Seawater, on average, has TDS concentrations of nearly 35g/kg. Extreme TDS values are found in highly evaporated lake or isolated seawater basins and in the deep subsurface (so-called "formation waters"), with TDS of nearly 350g/kg (35% salt solution!). We will focus here briefly on the compositions of potential drinking water sources (rivers and lakes) and the origins of the dissolved species.

Flowing water, whether in aquifers or streams, interacts with rocks and soils and slowly dissolves some of their chemical constituents. The pH (hydrogen ion activity) of the water determines the rate of dissolution and solubility of many chemical species. However, we will not discuss chemical processes in any detail here. Some chemical substances, particularly redox-sensitive trace metals (e.g. Fe, Mn, Pb, As and others), are more soluble when natural waters are depleted in dissolved oxygen (see the section called Contaminant Example 2 below). Most chemical species in natural waters have both natural and pollutant sources of many types (Table 1).

Natural waters also contained dissolved gasses. For example, carbon dioxide from the atmosphere is dissolved in water, and, through a series of chemical reactions, contributes to the total dissolved carbon in waters—primarily bicarbonate (HCO₃^2-). Gas solubility is inversely proportional to temperature and TDS. For example, dissolved oxygen solubility is shown as a function of temperature and salinity in Figure 1. Note that the amount of oxygen that can be held in fresh water decreases nearly 50% from near freezing temperature to 35°C. These are maximum concentrations, but natural waters can have lower dissolved oxygen concentrations as the result of biological activity such as the metabolism of water inhabitants, including bacteria. Photosynthesis of algae and aqueous plants can add oxygen to the water in which these primary producers grow. However, the breakdown of organic material by bacteria consumes dissolved oxygen. Thus, in waters below the surface wind-mixed layer (usually tens of meters or more) or in stably stratified lakes or bays, for which rates of oxygen replenishment to deeper depths are slow, deficiencies in dissolved oxygen can develop, with anoxia (total depletion of dissolved oxygen) at the extreme. Excess nutrient supply can have the same impact on a water body (eutrophication: see Module 1 and Contaminant Example 2: "Dead Zones" and Excess Nutrient Runoff) with deleterious effects on the aquatic biota.

Figure1. Dissolved oxygen (ml/L, or ppm) solubility (maximum expected concentration) in waters of different salinity (parts per thousand). Seawater typically has a salinity of 35 parts per thousand, whereas fresh water is near 0 parts per thousand.

Source: Michael Arthur, Penn State

There are, of course, many possible contaminants in drinking water supplies—in part natural, but also induced by human activities. There are three main groups of contaminants with relation to anticipated health effects:

1. Some contaminants produce no health effects until a threshold concentration is exceeded. Nitrate (NO₃) is an example of this; OK at 50 mg/liter (50 ppm), but at higher levels, it produces methemoglobinemia (e.g., "blue baby" syndrome).
2. The second group of contaminants has no apparent threshold for health effects. These include genotoxic substances. These include some natural and synthetic organic compounds, micro-organic compounds, some pesticides, and arsenic (see below) for example.
3. A third group consists of elements essential to the human diet: fluoride, iodine, and selenium are good examples—their absence in the diet causes problems, but an excess of intake can create problems.

Arsenic is a good example of both natural and human-induced contamination, and it is important as well because of its toxicity at higher concentrations (as are lead and fluoride). In recognition of the potential toxicity of arsenic (As), the US EPA lowered the MCL in drinking water from 50 ppb to 10 ppb in 2001. For example, check out this short video on possible health effects of arsenic and the need to have private wells tested.

Video: In Small Doses: Arsenic (10:01)

The health effects of arsenic.

In the western US, groundwater As levels are particularly high (see Fig. 2) because of the types of bedrock the groundwater moves through. The high concentrations in Maine are due to more alkaline (high pH), low dissolved oxygen groundwater that leads to high solubility of arsenic in shallow aquifers of glacial origin. Contamination of aquifers can also occur from agricultural runoff, runoff from arsenic-bearing wood preservatives, improper disposal of chemicals containing As, and/or mining activities. See this article in The New York Times, The Arsenic in Our Drinking Water, for a summary of possible health effects in the U.S. and Bangladesh.

Figure 2. A map of the US showing median arsenic concentrations (μg/L or ppb) in groundwater used to supply drinking water.

Source: U.S. Geological Survey

Global maps of the probability of arsenic concentrations in groundwater greater than 10 ppb can be viewed at Global fluoride and arsenic contamination of water mapped and is based on research by M Amini et al (Environ. Sci. Technol., 2008, DOI:10.1021/es702859e. A more generalized map of risk for As in drinking water can be seen in Figure 3.

Figure 3. Modeled risk of As in drinking water at significant levels from Schwarzenbach et al., 2010.

Source: United Nations Environment Program (UNEP)

A major issue in pollution of surface waters is the role that excess nutrient flows from polluted waterways into lakes, bays, and coastal zones play in creating excess biologic production in surface waters and dissolved oxygen at depth. In most cases, this nutrient-rich runoff results from agricultural operations, including the application of fertilizer to crops. Of course, such issues have already been briefly highlighted for the Chesapeake Bay in Module 1, but such so-called "Dead Zones" are globally widespread. It is, perhaps, easier to understand impacts on more restricted bodies of water (lakes, bays) with high fluxes of water from nutrient-laden rivers (such as the Chesapeake Bay setting). But, such issues also plague some coastal zones characterized by high river discharges. For example, the Gulf Coast "dead zone" has been recognized for over a decade and is attributed to high rates of nitrogen (and phosphorus) discharge through the Mississippi River system. Watch the following video from NOAA that provides a dead zone 'forecast' for 2019 and explains in general how dead zones form in the Gulf of Mexico and their impacts on the region.

Video: Happening Now: Dead Zone in the Gulf 2019 (1:59)

Dead Zone 2019 forecast and explanation

During summer, 2014, this area of hypoxia (less than 2 ppm dissolved oxygen in the water column near the bottom on the shelf) along the Louisiana and Texas coast was just over 13,000 km2 (>5000 mi2), somewhat smaller than that in 2021. Figure 7 illustrates the extent and severity of oxygen deficiencies during mid-summer, 2021. Coastal currents flowing westward mix and transport nutrients flowing from the Atchafalaya and Mississippi Rivers into the ocean.

Figure 7. Contours of dissolved oxygen near the bottom on the Louisiana and Florida shelves, July 25-31, 2021. Note deep red areas outlined in black indicating widespread hypoxia.

Source: NOAA

But how do high nutrient fluxes promote oxygen deficiency in coastal regions? The availability of nutrients in shallow sunlit waters near the coast allows prolific blooms of marine plankton (primary photosynthesis) which produces large amounts of organic matter. Nutrients can be a good thing and can benefit the entire food chain unless the fluxes of N and P reach an extreme termed "eutrophic" conditions. As the organic matter sinks to the bottom, it is a food source for consumer organisms (both in the water column and on the bottom), including bacteria. Shrimp, bivalve, and fish catches can increase to a point. In the extreme, the metabolism of fish, bivalves, bacteria and other critters consumes available dissolved oxygen in the water column faster than it can be replenished by mixing from above or laterally by currents. Also, because the coastal waters are warming during summer, they can hold less dissolved oxygen initially. As long as high nutrient fluxes continue the hypoxia expands and the organisms that depend on oxygen to survive either flee if they can swim, or die if they are more sedentary.

Observations of nearly 40 years indicate that the extent of hypoxia can wax and wane from year to year. In 2021, the Mississippi River saw increased discharge and nutrient runoff prior to the hypoxia event. In 2023, Louisiana coastal hypoxia was much less extensive and intense (Fig. 8, contrast with Fig. 7).

Figure 8. Contours of the dissolved oxygen near the bottom on the Louisiana and Florida shelves, July 23-28, 2023 (top). Bar graph of area in the Gulf of Mexico with hypoxia by year (bottom).

Source: NOAA

Previous research established a connection between runoff from agricultural operations in the mid-continent region into the Mississippi River drainage and development of hypoxia. Wet years (Fig. 9 corresponds to higher flow rates for the Mississippi River and greater delivery of dissolved nitrogen to the coastal region. Note that 1987-89 were years of low nitrate flux (Fig. 9), which correspond to low area of Gulf of Mexico hypoxia.

Figure 9. Nitrate flux from the Mississippi River scaled to Mississippi River flow rates (right y-axis in millions of cubic meters/y) to the Gulf of Mexico. Overall, there is a correlation between the two factors, particularly after about 1970. This study found a strong correlation between nitrate flux to the Gulf of Mexico, annual discharge to the Gulf, and fertilizer application over the entire drainage basin during the previous two years (r2=0.89).

Source: From Goolsby and Battaglin, 2000, USGS Fact Sheet 135-00

Figure 10. An estimated 5.5 million metric tons of nitrogen fertilizer were applied to croplands in the Mississippi River Basin during 1991.

Source: From Goolsby and Pereira, 1995; USGS Circular 1133

It is also clear from Figure 10 that very high rates of fertilizer application characterize the Mississippi River Basin. Think back to the section called Contaminant Example: Arsenic in Groundwater when you examined nitrate concentration variation in Iowa streams at present. It should be apparent that fertilizer applications and runoff are the main culprits in hypoxia in the Gulf of Mexico.

In this first part of Module 8, we will focus on current strategies for addressing water scarcity. In part, these strategies have arisen within the confines of water laws that have shaped the history of water access and allocation, especially in the American West. After a primer on this legacy that defines the "water allocation landscape", you will learn about the wide-ranging portfolio of approaches utilized by Los Angeles and Las Vegas - cities at the vanguard of creative and modern water management - to hedge against water shortage.

Introduction

As has been discussed throughout this course, the relationship between humans and water resources has a long and complicated history. Water has played a central role in how and where human civilizations have developed. Proximity to high quality, reliable water sources provides a firm foundation for a thriving society. Societies that have established near unreliable or unpredictable water sources that may dry up during droughts and/or flood unexpectedly and uncontrollably) have struggled and occasionally suffered catastrophic losses. In other cases, societies have suffered more chronic problems with water quality. Advances in engineering have greatly improved accessibility and reliability of water resources, to an extent that is difficult to overstate. In some cases, however, a combination of highly effective engineering and risky (or ill-informed) decision-making has created some sketchy and unsustainable situations, as discussed in the first half of this module. What does the future hold? How, when and where might the legacy of our past decisions cause us severe problems in the future? What new problems might we anticipate as a result of climate change and population growth? Will technology save us? Or will more ecosystem-focused planning provide a more resilient water future for humans? How much of Earth’s water should humans feel entitled to? How much should be left for nature? These are some of the questions we’ll address in part 2 of this module.

Goals

• Describe the two-way relationship between water resources and human society
• Synthesize data and information from multiple reliable sources
• Thoughtfully evaluate information and policy statements regarding the current and future predicted state of water resources

Learning Outcomes

In completing this lesson, you will:

• Analyze the political problems that arise when water supplies must be shared across borders

There are many examples of water disputes involving cross-boundary uses of shared resources. Three of these examples will be discussed in this section: The Nile River Conflict, The India-Bangladesh Ganges River Split, and The United States and Mexico— Sharing the Flow.

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
• Synthesize data and information from multiple reliable sources
• Communicate scientific information in terms that can be understood by the general public
• Identify strategies and best practices to decrease water stress and increase water quality
• Predict how the availability of and demand for water resources is expected to change over the next 50 years

Learning Objectives

By the end of this lesson, you should be able to:

• discuss the costs and benefits of desalination as a solution to water scarcity
• explain the benefits of water re-use
• describe the advantages and disadvantages of water optioning and water banking
• evaluate multiple approaches for safeguarding against water scarcity
• develop a portfolio of strategies for a water-poor urban area

In The Big Thirst, Charles Fishman repeatedly notes that while water problems are universal, they are fundamentally local and not global problems, in the sense that the issues are specific to a particular area, and excepting major water transfers, can most effectively be solved locally or regionally. Put another way, if you think back to Module 1, you’ll recall that if it were evenly distributed in time and space, the total precipitation that falls on Earth as part of the hydrologic cycle would be sufficient for water supply and dry land farming. The problem is not that there is not enough (or clean enough) water on the planet; it’s that the water does not fall when and where we need it. (see satirical article from the Onion)The fact that there is enough water globally does not help us all that much, because it is simply too expensive, impractical, and energy-intensive to move large volumes of water across oceans or between continents – though recent developments may challenge this mindset. Furthermore, the problems that face different areas are different: in Delhi, the major problems are related to water quality and infrastructure (i.e. Chapter 8 in The Big Thirst); in Las Vegas and Los Angeles, the problems are related to water scarcity and supply (Chapter 3); and in the Murray Basin or Perth, Australia, the problems are related to major shifts in supply and allocation in the face of changing climate (Chapter 7). Therefore, viable solutions are by nature local or regional – to obtain, manage, or treat water for a particular need and place. Potential Solutions to Problems with Water Scarcity and Quality

Here, we will briefly describe some of the most promising solutions on the horizon, many of which have been implemented as trials or in specific regions where the balance between demand and cost have made them feasible. We will also draw heavily upon readings from the textbook that you’ve completed for previous modules. For the assignment and activity linked to the module, we will ask you to develop a “portfolio” to secure future water supply for one of the population centers we’ve discussed in class (e.g., Las Vegas, Dubai, Los Angeles, etc…). This will require that you integrate much of what you’ve learned over the semester about precipitation patterns, surface water, and groundwater systems, water quality, water management and demand, cost, and infrastructure.

As you may remember from Module 1, the majority of Earth’s accessible water (i.e. not including a large amount of water trapped in minerals in the Earth’s interior!) is in the Oceans. In a sense, the Oceans would provide an unlimited supply of water, but of course, they are too salty to drink or use for most purposes. To use seawater for industrial, agricultural, or domestic/municipal supply, therefore, requires the separation of the water from the dissolved ions (mainly Na, Cl, Mg, SO₄, Ca, and CO₃). This can be accomplished in a variety of ways, but most commonly is done via either:

1. Distillation, in which the water is forced to evaporate and then collected, leaving behind a concentrated brine, or
2. Reverse osmosis, in which the water is forced through a semi-permeable membrane under pressure; the membrane physically excludes dissolved ions and other compounds, and only allows H₂O molecules to pass (Figures 1 and 2).

Of these, reverse osmosis (or seawater reverse osmosis, SWRO) has emerged as the more efficient approach, especially when scaled to produce the millions of gallons per day or more needed to meet the demands of even modest population centers.

Of course, removing the salt from seawater requires energy – and money. For that reason, it has been a subject of intense research and engineering efforts, in order to reduce costs through increased scale, improved efficiency, pre-filtration, and improved materials (most importantly, advances in membrane materials that require less pressure to push the water through but still exclude dissolved ions). Early desalination plants were restricted to a relatively small scale, and mainly in desert areas (e.g., the Middle East), or to meet water quality requirements for the CO river treaty of 1944 (e.g., the Yuma desalination plant in Yuma, AZ, brought online in 1997). However, with improving efficiency, increasing demand, and perhaps spurred by drought, desalination is now emerging as one potential viable solution, at least in areas with access to the ocean, and the economic resources to construct and operate the plants.

Figure 1. Photo of a desalination plant. Blue cylindrical coils in the background are reverse osmosis membranes wrapped around pipes that force the water outward under pressure.

Source: James Grellier (Own work) [CC BY-SA 3.0 or GFDL], via Wikimedia Commons

Figure 2 Diagram of a typical SWRO plant process. Click for a text description

Initial Chemical treatment with initial solids removal to traveling screens with filter out shells, wood, and other debris greater than ¼ inch. Then particle settlement: heavier solids are settled and removed from the water, then smaller solids are filtered from the water through sand filters, a diatomaceous earth filter is used next to remove microscopic materials. Any water removed from solids is recycled. Water is then transferred to cartridge filters which are in place to protect reverse osmosis membranes. It then goes through two passes of the reverse osmosis process where the water is put under high pressure and pumped through ¬¬sacks housing reverse osmosis membranes to remove the salt. It then goes to post-treatment and a holding tank.

Source: Tampa Bay Water and appears on NOAA

As we’ve already seen in Module 8, one increasingly viable strategy to address limited water supply is that of treatment and re-use. This can take a variety of forms, including reclamation and re-use of wastewater for industrial or consumptive applications like golf courses or parks, or treatment of wastewater to meet drinking water standards and re-use for domestic/municipal supply. The former constitutes a major element of Las Vegas’s approach to maximizing their limited allocation of CO river water from Lake Mead. The latter is becoming increasingly – though not universally - accepted as a way to increase supply, and has been implemented in several areas, including Orange County and even at Penn State!

The Orange County Groundwater Replenishment System (GWRS) is one well-known case study of wastewater reclamation for municipal supply at a relatively large scale (Figures 5-7). The GWRS plant is a 70 million gallons/day facility (72,000 acre-feet/yr) and generates enough potable water for ~500,000 people. The facility also solves the secondary problem of managing effluent to the ocean because much of the wastewater that would otherwise be discharged offshore is captured and re-used. The facility takes advantage of proximity to the wastewater treatment facility to allow for low-cost and efficient “on-site” treatment and uses gravitational energy to transfer the water for treatment. The cost of the facility was subsidized by grants. With the subsidy, the cost of treated water is \$400-500/acre-foot; even without the subsidy, the cost is competitive with imported (CO River) water at \$800/acre-foot.

Figure 5. Photo of reverse osmosis coils at the Orange County GWRS facility.

Source: K. Ross

Figure 6. Professors Arthur and Saffer

Source: M. Ren.

Figure 7. Student L. Wandel sampling the treated wastewater at the GWRS at the end of a facility tour.

Photo credit: M. Ren.

Two key advantages to reclamation and re-use are: (1) the supply is by definition local, in that it was used by the same people who would use it again, and has already been captured for treatment. This substantially reduces the need for infrastructure and conveyance, and thus is highly efficient and reduces cost; and (2) the total dissolved solids (TDS) in wastewater are much lower than in seawater, such that the energy and cost are low in comparison to SWRO (Figure 8).

Figure 8. Summary of energy intensity, or “cost”, for various water supply sources in California as of 2012. Click here for a text description

Energy sources as of 2012

Type	kWh per million gallons (range)
Seawater desalination	13000-17000
Imported water (state water project/So. Cal)	8000-15000
Imported water (CO river aqueduct/So. Cal)	6000
Recycled water (membrane treatment)	3000-8000
Brackish water desalination	1000-9000
Imported Water (Northern California)	0-3000
Recycled water (tertiary treatment)	1000-2000
Local surface water	0-1000

Source: H. Cooley, “Desalination and Energy Use…Should We Pass the Salt?”, May 28, 2013.

Another more local example is that of the Penn State “Living Filter”, which has been in operation since the early 1960s, and in full-scale operation since the mid-1980s. The treatment facility captures approximately 2.5 million gallons per day (the total water use on campus at the University, plus a small proportion of water used by residents of the nearby Borough of State College). This water is originally sourced from a fractured limestone aquifer that underlies the region. Rather than treating the wastewater and discharging it to local surface waters (Spring Creek), the water undergoes primary and secondary treatment, followed be de-nitrification and minimal chlorination to ensure that any (unlikely) remaining pathogens in the water are killed, and then spray application in the aquifer recharge area. After treatment, the biological oxygen demand has been reduced by 95-99%. The term “living filter” refers to the thick (>50-75 foot) soil column that overlies the aquifer; the combination of physical processes in the soil, natural degradation by exposure to soil acids and UV, and microbial activity effectively “filter” the treated wastewater to meet drinking water standards. In total, the system is almost 100% efficient in the re-use of extracted groundwater, with ~1 billion gallons of treated water per year recharged to the aquifer.

Of course, there are some obvious drawbacks to water re-use, though these are arguably mostly psychological and rooted in the so-called “Yuck Factor”. It is easy to forget that water is the ultimately reused product. The water in our rivers and oceans has certainly cycled through many organisms over the course of its history (think “dinosaur pee!”). The surface water that we think of as “clean” and which has historically been the dominant water supply for human consumption, hospitals, laundry, and other uses, is mixed with discharged treated wastewater from upstream communities. For that reason, we treat surface water before use. In this sense, why or how is directly treated wastewater any different? Likewise, rural domestic wells are often down-gradient of septic systems or leach fields, albeit a safe distance to allow natural degradation and filtration in the soils and aquifer system. Fundamentally, this raises the question of whether we would rather drink and do our laundry with water that was once our own wastewater, or somebody else’s.

As we covered in Module 8, one additional hedge against fluctuation in supply, and/or against climate change, is to purchase, trade, or bank water, either using one’s own allocated water in times of surplus or through the purchase of someone else’s unused water rights in a given time period. For example, Las Vegas has adopted this strategy to provide alternate sources in times of severe water shortage, through agreements with Arizona and California. These agreements are one means to transfer water, either actually or virtually, from areas where it is available (in surplus or actively stored in aquifers) to those where it is needed.

More sophisticated arrangements have also been explored, in which water is treated as a commodity and with prices determined by demand. One example of this is described in the High Country News piece "LA Bets on The Farm". The basic concept is that the MWD of Los Angeles pays farmers with water rights for irrigation to fallow some portion of their land. Because, at least currently, there is no shortage of food, the exchange works: LA gains an additional water supply, and the farmers or irrigation districts make a bit of money (without having to take on any risk associated with growing crops, commodity prices, or the like). A more recent iteration of the agreement provides both parties with additional flexibility to account for unpredictable precipitation patterns and water supply, whereby the MWD purchases “options” to the water rights for $10/acre-foot. By March of that particular year, the MWD must decide whether they will take the water or not. If they do, they pay an additional $90/acre-foot (enough that the irrigation districts make some money); if not, there’s still time to plant crops, and the irrigation district keeps the option fee.

At their core, these approaches use the market to define the pricing of water and to shape the terms of agreements that will be mutually beneficial. In part, they work because the amount of water needed for irrigation far exceeds that for municipal or domestic uses (see Module 1). And in part, they work because the irrigation districts receive water that has been heavily subsidized, largely through public investment in major infrastructure that underlies the water systems. Ultimately, however, it is not clear that the exchange or purchase of water rights will really work in the face of severe drought, major climate changes, or continued increases in demand. After all, these strategies are essentially a form of regional water re-allocation or transfer – but in a zero-sum game, they can only work if there is enough surface water or groundwater to be had.

Recognition that these strategies may ameliorate shortages and can serve as a valuable hedge against variability in supply, but are unlikely to fully solve problems of water scarcity if we insist on continued development in water-poor regions, has led to large-scale proposals to transfer water or exchange water rights over great distances and across borders. For example, as discussed briefly in Module 8.1, and in Chapter 3 of The Big Thirst, Las Vegas has begun to explore distant sources of water. These include groundwater in Central and Northern Nevada (a project currently underway), as well as proposed exchanges in which Las Vegas would bankroll desalination facilities in Coastal California, and trade the “new” supply of desalinated water for withdrawal of the same amount from Lake Mead. As described in the next section, the basic fact that there is water available if one reaches far enough – and is willing to pay for it - has led to all manner of proposals to move water across oceans and continents. To an extent, this calls into question Fishman’s assertion that all water problems and their solutions are “local”.

If you have ever carried your water on a camping or backpacking trip, you know first hand that water is heavy, and therefore that transport is costly and energy-intensive (that’s why there is a market for water filters and iodine tablets!). For example, almost 20% of electricity in California is used for the water-related activity, and much of that to move water across the state. Despite the high energy and economic cost to transfer large volumes of water, it remains the only – and ultimate – hedge against uncertain supply. As you’ve heard from Marc Reisner and George Miller in the Cadillac Desert films we’ve watched, the idea behind many ambitious water proposed water projects in the Western US, many of which never reached fruition, was to “go where there was so much water, you’d never run out”, and construct “pipelines beyond the wildest imagination”. Patricia Mulroy has even suggested that water transfers from the Great Lakes to the American Southwest should be considered in order to serve the greatest good; water rights and export form the Great Lakes watershed is, not surprisingly, a controversial topic.

In most instances, large-scale water transfers over huge distances by pipeline or tanker are simply too expensive to make sense, or there is too much political resistance. As one extreme example, in the early 1990s, Walter Hickel (then governor of Alaska) and California congressmen Edward Roybal and George Brown requested a feasibility investigation for a pipeline that would bring water from Alaska to California through a subsea pipeline (Figure 9). The committee estimated that the cost of water transfer would be between $3000-4000 per acre-foot, or approximately triple to quadruple the cost of SWRO desalination. In the same report, the committee assessed other sources of water for California and noted that bringing water in by tanker would cost $1,500-2,000 per acre-foot for contracts of at least 30,000 acre-feet.

Figure 9. Map showing proposed pipeline route to bring water from Southern Alaska to California.

Source: U.S. Congress, Office of Technology Assessment, Alaskan Water for California? The Subsea Pipeline Option Background Paper, OTA-BP-O-92, Washington, DC: U.S. Government Printing Office, January 1992.

In other cases, the economics are not as prohibitive. For example, water is routinely transferred within California, or between Western States (e.g. Colorado River water transferred to Southern CA in the All American Canal) over distances of hundreds or even over a thousand km. This so-called “imported water” is the basis for the cost comparison of alternative supplies. At a yet larger scale, China has recently undertaken the world’s largest water transfer project, the South-to-North Water Diversion Project (or SNWDP). The main driver for the water project is that precipitation, and thus water resources, are very unevenly distributed across China (Figure 10) – and water-scarce provinces account for over 40% of the GDP. At the same time, almost a third of the population (300 million people) have access only to contaminated water – largely because of insufficient clean water supply and/or limited surface water flows that do not flush pollutants from the channel (as discussed in Module 5 – sidebar on the Three Gorges Dam).

The SNWDP will move almost 45 billion m³ of water per year (36 million acre-feet, or ~3 times the Colorado River’s flow), over distances of almost 4500 km. Although the financial benefits seemingly outweigh the costs – and hence the project is moving forward – major drawbacks are inevitable. For example, such a large water transfer is likely to have major impacts on river systems, in terms of changes in flow, sediment transport, and flushing; relocation of people along the route; construction across archeological and religious sites; and environmental impacts on wetlands that may disappear and endangerment of species that have adapted to the natural river flow regime (sound familiar? think back to Modules 3, 4, and 5!)

Figure 10. Map of average annual precipitation in China (from Creative Commons).

Source: "China average annual precipitation (en)," Original from Wikimedia Commons: by Alan Mak for Wikipedia, the free encyclopedia. Derivative work: Cybercobra (talk). Licensed under Creative Commons Attribution-Share Alike 3.0 via Wikimedia Commons.