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Water Resources & Supply
Water is Nevada's most precious resource and more than any other will determine Nevada's future. Wise management of water resources and protection of water quality is vital to the state's economic future and quality of life. Finding ways to stretch water supplies for new beneficial uses while maintaining existing beneficial uses is perhaps the biggest challenge confronting Nevada. The Nevada State Engineer, in the Nevada Division of Water Resources (NDWR), administers state water law. The mission of NDWR is to conserve, protect, manage, and enhance Nevada's water resources through the appropriation and reallocation of the public waters. All surface and underground waters within the state belong to the public (Nevada Revised Statute 533.025).
Surface waters are limited and essentially fully committed. Ground water resources are approaching full commitment in the state's southern and western regions. In the fast growing counties,  obtaining water to meet additional municipal or industrial uses requires the developer to purchase and obtain a permit to transfer water rights from agricultural uses. About three-fourths of the water withdrawn from surface and groundwater is used for agriculture (Figure 2-1). Negative consequences may result from agricultural water rights transfers. For example, browning of fallowed farmland and irrigated greenbelt areas (e.g., pasture, artificial meadows and riparian zones) can lead to nuisance weed cover, erosion of barren soil, and lost wildlife habitat.
Awareness is growing that active management of water resources can improve supplies and quality, as indicated by an apparent increase in the number of stream channel, wetland, watershed, and groundwater recharge projects. Conservation also can extend limited water supplies, although a comprehensive state strategy has not been developed. However, municipal and industrial suppliers in Las Vegas Valley and Truckee Meadows are making progress, as are the Truckee-Carson and Pershing County irrigation districts. Only municipal suppliers are required to adopt a conservation plan. In any event, without periodic reporting, the status of conservation plans and achievements cannot be estimated.
Surface Water
Nevada's major rivers are shown in Figure 2-2. Surface water is the source of 60 percent of the total water supply
used, and 72 percent of the residential, commercial, industrial and public use. The Truckee River and Colorado River provide drinking water for approximately 85 percent of all Nevada residents (i.e., Washoe and Clark county urban areas). Streamflow primarily comes from annual snowfall and melt, though groundwater flow may also augment flow in rivers and creeks where underground water bodies (aquifers) are connected to channels.
Annual and seasonal variation in surface water flow can be large. Maximum stream flow often occurs in May or June (peak snowmelt). With one exception, most of the flow in Nevada's major rivers originates in other states. Headwaters of the Carson, Truckee, and Walker rivers lie in California, and the Colorado River carries water from several Rocky Mountain States. The exception is the Humboldt River, which begins and ends in Nevada. Flow in the major rivers and streams follow a typical pattern. River channels gain most of the flow in the mountains, and then lose it as the channel traverses drier valleys. Stream flow losses come by evaporation, vegetative transpiration, percolation, and diversions for beneficial uses. Water diverted for off-stream uses and not consumed by crops, people, or industry, and subsequently delivered back to the  stream of origin is called return flow. Return flow is a vital component in the water use cycle, because the practice provides some assurance that water will be available for use in lower reaches.
The estimated average annual yield from rivers and streams in Nevada is approximately 3.2 million acre-feet per year. For 1995, the estimated surface water withdrawals totaled 2.4 million acre-feet (Nevada Division of Water Planning, 1999a). About 1.9 million acre-feet originate in Nevada watersheds, and about 1.3 million acre-feet flows in from and 0.7 million acre-feet flows out to adjoining states.
Surface waters have been fully appropriated for many years, though in wet years surplus water may be available. Streamflow reaching terminal basins can replenish lakes and wetlands that support a variety of habitat types, fishes, and wildlife; recharge groundwater; improve water quality; and provide outdoor recreation opportunities. Most priority rights for surface water in Nevada were established in the 1800's. Rights to use water for irrigation date back to the 1850's in streams draining the Sierra Nevada Range and to the 1870's and 1880's in the Humboldt River Basin. Additional dams and reservoirs would be needed to impound the water to detain surplus flows for later use.
 Next Page -- Major Rivers, Lakes, and Reservoirs
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