Our current water supply
Southern Nevada gets about 90 percent of its water supply from the Colorado River, which begins as rain and snowmelt in the Rocky Mountains. The river serves about 40 million people across seven western states and the country of Mexico. The river is governed by a series of compacts, laws, court decisions, rules and treaties, collectively known as the "Law of the River."
Nevada has the right to consumptively use 300,000 acre-feet of water per year. Consumptive use is defined as water withdrawals (or diversions) minus any water that is returned to the Colorado River. These returns are also known as "return-flow credits."
The Colorado River has endured nearly 20 years of severe drought, which has reduced the amount of water in Lake Mead. If Lake Mead water levels continue to decline, a shortage will be declared and the amount of water available to Nevada and other water users will be reduced.
Nevada is not currently using its full Colorado River allocation and a shortage declaration is not expected to impact current water users, but water conservation remains an ongoing priority.
Las Vegas Valley groundwater
About 10 percent of Southern Nevada's municipal water supply comes from Las Vegas Valley groundwater. Groundwater is pumped from the underground aquifer, which is fed by rain and snowmelt from the mountains surrounding the Las Vegas Valley.
Our community relied on local groundwater supplies to meet most of its water needs until the early 1970s, when facilities to treat and deliver Colorado River water were constructed. Today, this water source remains a critical component of our community's water resource picture.
The Las Vegas Valley Water District and North Las Vegas, member agencies of the Southern Nevada Water Authority, have permanent groundwater rights totaling 40,760 acre-feet and 6,201 acre-feet, respectively. The two entities operate about 100 permitted municipal wells in the Las Vegas Valley.
The Water Authority developed and manages the Las Vegas Valley Groundwater Management Program to help protect the Valley's groundwater basin from being overdrawn and potential sources of contamination.
With return-flow credits, Nevada can divert more than 300,000 acre-feet per year, so long as there are enough flows returned to the river each year that our consumptive use is no greater than 300,000 acre-feet of water per year. Return-flow credits expand Nevada’s Colorado River allocation by approximately 75 percent.
Reuse and recycling
Approximately 40 percent of the water in the Water Authority's service area is used indoors. Of the water used indoors, about 99 percent is recycled and returned to our water system. The City of Boulder City, City of Las Vegas, Clark County Water Reclamation District, City of Henderson and City of North Las Vegas each operate wastewater treatment facilities that contribute to the region’s reuse and recycling efforts.
Direct reuse involves collecting, treating, and reusing wastewater flows for non-potable uses such as golf course irrigation or parks use.
The Water Authority's Cooperative Agreement allows for up to 22,000 acre-feet per year of water of direct reuse. Actual reuse varies from year-to-year. Additional direct reuse does not extend Nevada's Colorado River allocation because it will reduce or offset the amount of water returned to Lake Mead, for return-flow credit.
Indirect reuse consists of recycling Colorado River water for return-flow credits. Water used indoors is captured by the sanitary sewer where it is highly-treated and returned to the Colorado River via the Las Vegas Wash, which flows into Lake Mead.
Water that is used and/or wasted outdoors evaporates and cannot be used again. This is "consumptive use" as the water was consumed and cannot be reused.
Conservation as a resource
Water conservation is a cost-effective resource that helps reduce current and future demand for water. Like water reuse and recycling, water conservation helps stretch our community’s available water supplies, especially during drought, by freeing up water that is used inefficiently or wasted.
Southern Nevada recycles all water used indoors through direct or indirect reuse. But water that is used outdoors cannot be captured, treated or used again—this is a consumptive use of water because the water is fully consumed by plants, grass and evaporation.
Conservation rebates and coupons are designed to help local residents and businesses reduce water waste and consumptive water use. SNWA's Water Smart Landscapes program has helped our community remove and replace water-thirsty turf, saving billions of gallons of water for our community.
Water conservation through compliance to mandatory watering restrictions also has saved billions of gallons.
How Colorado River water is allocated
A complex body of laws, court cases, and regulations known as the "Law of the River" control the use of Colorado River water and the operation of its dams.
In the 1800s, states diverted water from the Colorado River and its tributaries without restrictions. As the diversions increased, a long battle over apportionment evolved. Today, the Colorado River is among the most controlled, controversial, and litigated rivers in the world.
Nevada receives 300,000 acre-feet per year of Colorado River water under the Law of the River compacts. An acre-foot is equivalent to 325,851 gallons of water.
At the time of the 1928 Boulder Canyon Project Act, negotiators felt 300,000 acre-feet was more than enough. Southern Nevada had no significant agricultural or industrial users, groundwater seemed plentiful, and the area’s small population was not anticipated to grow significantly. Negotiators focused instead on hydro-electricity and secured one-third of the electricity generated by Hoover Dam.
The compact also referenced Mexico's right to Colorado River water. In 1944, the United States signed a treaty in which it agreed to deliver an annual quantity of 1.5 million acre-feet per year to Mexico.
Colorado River apportionment
In 1922, seven western states negotiated the Colorado River Compact, which divided the states into two basins: Upper Basin and Lower Basin. The Upper Basin includes Colorado, New Mexico, Utah and Wyoming. The Lower Basin includes Arizona, California and Nevada.
A total of 16.5 million acre-feet per year are apportioned amongst the seven states along the Colorado River, plus Mexico.
Average river flows
Compact negotiators estimated the flow of the river to be at least 17 million acre-feet of water per year and allocated 16.5 million acre-feet of water per year for use by the seven western states and Mexico.
Today's records indicate an average flow of 14.9 million acre-feet of water per year at Lee's Ferry, just below Lake Powell.
Consequently, the sum of the actual compact apportionments and the Mexican treaty exceed the flow of the river in most years.
In addition, a sustained drought has reduced significantly the average runoff into the Colorado River.
Despite the reduction in water flowing into the river, there is little support among the seven states sharing the water to renegotiate the compact.
A new agreement would require approval from each state’s legislature and the U.S. Congress.