In the mid-1800s, early settlers named the area "Las Vegas", Spanish for "the meadows", because the Valley, fed by the Las Vegas Springs, was lush, grassy, and green. The springs yielded approximately 5,000 acre-feet of water per year. As you may recall, this is about the amount of water needed today to support 5,000 families of four, or a population totaling around 20,000. With a plentiful natural water supply, Las Vegas became a key stop and hub for the railroads: first the San Pedro, LA, & Salt Lake City Railroad, and later the Union Pacific.

In the early 1900s, private wells drilled into the valley-fill confined aquifer became commonplace to augment the spring flows, as residents tried to turn the valley into productive farmland. Many of the wells were artesian but were left uncapped (Figure 7). By 1912, the 1000 residents of Las Vegas withdrew about 22,000 acre-feet of water per year from the springs and aquifer. By 1930, a combination of several dry years and increasing demand led to overdraft conditions. In the meantime, the Colorado River Compact of 1922 allocated a small amount of Colorado River water to Southern Nevada (see Sidebar: CO River Compact). However, Las Vegas continued to rely principally on groundwater, and aside from some industrial uses, the Colorado allotment went largely unused until the 1940s. (Note that Hoover Dam, the primary infrastructure that allows surface water storage and withdrawal for Clark County, was not completed until 1936.)

Figure 7. Photo of the Eglington Well in Las Vegas flowing at approximately 615 gallons/minute (ca. 1912). The well, like many others in the Las Vegas Valley, was artesian when first drilled and was left uncapped.

Source: U.S. Geological Survey Circular 1182

With a steadily growing population and water demand, withdrawals greatly exceeded natural recharge and overdraft of the aquifer worsened. In an effort to reduce groundwater extraction, the Las Vegas Valley Water District was created in 1947, in part to begin using the Colorado River allotment. Despite these efforts, by 1960 the valley’s population had swelled to over 110,000, and almost 50,000 acre-feet of water were extracted from the aquifer annually. The natural springs dried up in 1962, and sustained overdraft led the potentiometric surface to drop by a few feet per year on average. The pattern continued through 1971 until the Southern Nevada Water System began delivery of Colorado River water from Lake Mead for municipal supply – 24 years after the water district was created.

With a plentiful supply (300,000 acre-feet per year) of Colorado River Water ready for delivery and distribution, population growth accelerated, reaching almost 700,000 by 1990 (Figure 8), and about 2 million by 2012. Coincident with the shift to water supply from Lake Mead in 1971, dependence on groundwater gradually started to decline (Figure9). As discussed in more detail below, managed (induced) recharge of the groundwater system using surplus Colorado River water was begun on a small scale in the late 1980s; this “banking” of water in wet years or times of surplus is viewed as one strategy to cope with water shortages.

Figure 8. Map showing land use and the growth of the Las Vegas metropolitan area from 1972 to 2010.

Source: NASA Visualization Explorer

Figure 9. Water use in Southern Nevada from 1900 to 2008. Note that groundwater use started to decline and surface water use increased steadily from 1971 onward when the distribution of Colorado River water for municipal use began. Prior to that, CO River withdrawals were limited to a few industrial uses. Note that from around 1990 to present, withdrawals from Lake Mead have exceeded Nevada’s 300,000 acre-foot allotment (see text).

Source: SNWA water resource plan, 2009.

Currently, about 90 percent of Southern Nevada’s water comes from Lake Mead (the Colorado River) (Figure 9); the rest comes from groundwater. Because of the very limited natural recharge to the aquifer system, and the fact that no other surface water is available, Las Vegas depends almost exclusively on the Colorado River to sustain its population and economy. The city is essentially at the mercy of the Colorado River. When the Colorado River Compact was signed in 1922, the allotment of 300,000 acre-feet per year was viewed as generous for the sparsely populated state. However, as may sound like a familiar story, with a rapidly growing economy, combined with good weather and apparently plentiful water, population growth rapidly exceeded most projections (see Figure 5).

Of the water delivered by the Southern Nevada Water Authority, it may be surprising to note that most (almost 60%) goes to residential use (Figure 10). Of this, a large fraction is used consumptively for watering lawns. As discussed in detail in The Big Thirst, incentive programs for removal of turf from parks, common areas, and residences is one strategy to reduce water use. Golf courses and resorts, which are often the stereotypical poster children for water “waste” in Las Vegas, use about 14% combined.

The pie chart shown in Figure 10 provides the first blueprint for conservation efforts and potential re-use, by identifying the key water uses in the district. Moreover, there is also a recognition that not all water uses are “equal”: some require clean water (i.e. residential uses, many industrial uses, medical), whereas others do not (golf courses, parks). As a result, reclaimed and partly treated water may be used for many needs. In Las Vegas, water re-use – essentially getting two uses of the same water - is one part of a diverse strategy to maximize the limited allocation of Colorado River water (additional detail on treatment facilities and pricing for reclaimed water are described on the water district’s website.

Figure 10. Municipal water uses in Southern Nevada as of 2022.

Click for a text description

Residential (single-family): 43.3% Residential (multi-family): 16.3% Commercial/Industrial: 14.4% Golf Courses: 5.1% Resorts: 6.3% Common areas: 6.5% Schools/Government/Parks: 6.3% Other: 1.8%

Source: SNWA water resource plan, 2022.

Due to a decades-long drought in the Colorado River system (see Sidebar: CO River Compact), the water level in Lake Mead has dropped by almost 170 feet since 2000 (Figure11). This corresponds to a decrease from ~25 million acre-feet of stored water to around 10 million acre-feet. If the lake water level drops to 1075 feet (as of June 2022, it is 1043 feet!), a federal shortage would be declared, triggering a reduction in Nevada and Arizona's allocations. In June of 2022, the U.S. Bureau of Reclamation decarded an emergency request for Colorado River states to reduce use by 2-4 million acre-feet within 18 months.To make matters worse, the two intakes in Lake Mead that withdraw water for Las Vegas cannot function if the lake level drops below 1050 feet (intake #1) or 1000 feet (intake #2). With the possibility of continued dry conditions, and because of their near sole dependence on Colorado River water, Las Vegas has developed a multi-pronged strategy to hedge against uncertainty due to future climate change coupled with likely increased demand due to growth and development in Clark County.

Figure 11. Photo of Lake Mead, facing upstream, taken from the Arizona side of Hoover Dam (ca. 2009). The white “bathtub ring” is caused by bleaching of the rock, and marks the previous high water level approximately 140 feet higher than today.

Source: Demian Saffer

As you have read about in The Big Thirst: Dolphins in the Desert, Las Vegas has been aggressive in water conservation efforts. Part of these efforts focuses on simple reductions in household water use through education, regulation (i.e. watering restrictions), and incentivized removal of water-intensive landscaping. The city has also implemented GPS technology and pressure and acoustic sensors to monitor leaks in their pipelines to limit leaks and thus maintain high efficiency. As a result of these efforts, per capita, water use in Las Vegas has decreased substantially over the past 20 years or so, from over 340 gallons per day to less than 200 gallons (a 40% reduction!) (Figure 12). The SNWA has set a conservation target of 105 gallons per day fro 2035. As a result, Southern Nevada's total annual water use dropped by almost 90000 acre-feet (30 billion gallons) from 2002 to 2012, even as its population grew by 400,000.

Additionally, as noted above, Las Vegas treats wastewater for re-use, especially for applications that (a) don’t require high-quality water, like watering golf courses and parks; and (b) are consumptive. Re-use, incentivized by lower pricing, effectively allows the same water to be used twice, thus making the modest allotment of Colorado River water go further. Indeed, although Southern Nevada’s gross withdrawals from Lake Mead are almost 600,000 acre-feet per year (Figure 9), this is offset by the return of treated water to the Lake such that net withdrawals (consumptive use) remain at the 300,000 acre-feet limit.

Figure 12. Historical (blue) and projected (red) per capita water use in Southern Nevada.

Source: SNWA water conservation plan, 2014-2018.

Despite a history of overdraft in Las Vegas itself, Southern Nevada has recently turned its eyes back to the underground as an additional water source – but this time in sparsely populated valleys to the North and Northeast of Clark County (Figure13). The rationale for the SNWA’s “Groundwater Development Project” is that groundwater recharge is partly a function of the area over which infiltration occurs, so distributed withdrawals of groundwater from several large valleys fill aquifers outside of Las Vegas may be more sustainable than focused withdrawals from only the local aquifer system. Additionally, the targeted aquifers are in sparsely populated areas, with relatively small water demand.

Nonetheless, as you might imagine, there has been strong opposition to the plan from both environmental groups and ranchers and residents of these valleys, especially when considering past examples of the annexation of water rights for large cities (e.g., Los Angeles and the Owens Valley) and the negative outcomes for the local communities.

Figure 13. Map showing regional groundwater flow systems in Nevada and Utah.

Source: USGS Water Sources of the Basin and Range

As another hedge against water shortage and climate change, the Southern Nevada Water Authority has entered into a series of “Water Banking” agreements with other the Lower Basin Colorado River states, Arizona and California. In these agreements, Nevada pays the other Colorado River water rights holders to store unused water in times of surplus by injecting it into aquifers. Nevada then receives credits for the stored water; if the water is needed, Nevada uses the credits to draw the equivalent water from Lake Mead, and in exchange, the “banker” withdraws the same amount from the aquifer. Although pumping is energy-intensive, groundwater banking does not require the construction of large reservoirs, and the water is not subject to large evaporative losses.

In its water banking agreement with Arizona, the SNWA paid \$100 M initially and began making yearly \$23 M payments in 2009 that will continue indefinitely. The agreement allows the SNWA to withdraw up to 40,000 acre-feet per year. In 2004, SNWA also began a water banking agreement with the Southern California Metropolitan Water District (the water district that serves L.A.) in which some of Nevada’s surplus Colorado River water is stored in an aquifer in Southern California. The agreement allows the SNWA to withdraw up to 30,000 acre-feet per year, provided that they give 6 months notice. Since 1987, Southern Nevada has also been banking its own surplus water – when available - in the valley’s aquifer for later use if needed. In Nevada, about 333,000 acre-feet have been stored through 2022, and in Arizona’s aquifer, the SNWA has stored 614,000 acre-feet of the Colorado River’s water through 2023.

In 2005, faced with the specter of prolonged drought and projected Lake Mead water level declines, the SNWA board of directors approved construction of the so-called “Third Straw”, a new $812 M intake from Lake Mead that would allow Southern Nevada to physically extract water from the lake at water levels as low as 1000 feet above sea level (Figure 14). Construction of the intake involves boring a 23-foot diameter tunnel through 3 miles of rock, with much of its length beneath one of the Earth’s largest man-made reservoirs!

The new intake will intersect the lake at 860 feet above sea level but will share a pumping station with intake #2, so will only be able to operate at water levels of 1000 feet (the same as for intake #2). The primary purpose of the third straw is to maintain overall system capacity if Lake Mead falls below the 1050 ft water level limit for operation of intake #1. It also will access the deepest parts of Lake Mead, where water quality is highest. The initial plan for the third intake included a separate pumping facility but was removed to cut costs. It is always possible that the $200 million pumping station and pipelines could be added in the future, though if the Lake Mead water level were to drop much below 1000 feet, there would be much bigger problems throughout the lower Colorado River basin.

Figure 14. Figure showing projected water levels in Lake Mead as of 2023, with levels shown for federally declared shortage and operational limits of the SNWA intakes.

Source: SNWA Water Resource Plan, 2023.

Figure 14 shows the elevation of Lake Mead on the y-axis versus the year on the x-axis including different water conservation projects. The important take home from this figure is that as we near 2022 we see that water levels drop. But as different conservation projects (in green, pink, purple, etc.) grow, the rate at which water levels drop decreases. In the time series, the thick dashed line represents the hypothetical elevation of Lake Mead due without conservation projects, while the solid black line represents the actual water level. Although water level is still dropping as of 2022, conservation efforts play a large role in stabilizing Lake Mead water levels.