California Water Use

from the CA Department of Water

Every five years the U.S. Geological Survey (USGS) compiles and publishes national water-use estimates for each state and the United States as a whole. Over time these snapshots of water use can identify trends within the states. In response to the severe drought in California, the worst in modern records, the USGS has released the 2010 water-use estimates for California early- ahead of the other states. These water-use estimates are important to state regulators and water managers who use the data as inputs to their hydrologic models that they use for water resource planning and management. The water use estimates combined with the hydrologic models can help water managers, regulators and elected officials assess the changing demographics, land use, irrigation practices, climate, and water availability impact water use and the economy of the state. So, hot off the presses here is what the 2010 data shows.

Total waster use in California fell from 2005 to 2010. According to the USGS, 38 billion gallons per day (42,000,000 acre-feet per year) of water were withdrawn from groundwater and surface-water sources in 2010 while 46 billion gallons per day (52,000,000 acre-feet per year) in 2005. Overall, water use in California decreased by 17%. In 2010, Californians withdrew an estimated total of 38 billion gallons per day (42,000,000 acre-feet per year), 25 billion gallons per day (28,000,000 acre-feet per year or 67%) were supplied by surface water and 13 billion gallons per day (15,000,000 acre-feet per year or 33%) was supplied by groundwater. In 2005 35 billion gallons per day (39,000,000 acre-feet per year or 76%) was supplied by surface water and 11 billion gallons (12,000,000 acre-feet per year or 24%) was supplied by groundwater. California has increased their dependence on groundwater between the two dates, but that could have been caused by the lingering effects of the 2007-2009 drought. In California 2005 was in the middle of the last wet period.

from USGS

The California drought of 2007-2009 was ending in 2010, however while most farmers in the Central Valley got their full federal water allotment that year, the west side of the San Joaquin Valley did not receive full water allocations. The state water project allocation remained well below normal that year. At the time the state officials attributed the reduction in a wet year to strict pumping curbs in the Sacramento-San Joaquin Delta, to protect salmon and smelt populations, and because Oroville has been slower to refill than some other reservoirs. The increased use of groundwater between 2005 and 2010 could be a trend or it could simply be that groundwater was used to make up the shortfall by the farmers in the west side of the San Joaquin Valley. The variations in rainfall that California experiences allow the state to struggle from wet period to wet period without planning for the future.

from USGS

A significant portion of the 17% reduction in daily water use between 2005 and 2010 was from a reduction in thermoelectric water use. Only about 82% of water withdrawals, or 31 billion gallons a day in 2010 were fresh water, the rest was saline water. In California 95% of saline water withdrawals are used for thermoelectric generation (most of the rest for aquaculture). In 2005 72% of water withdrawals or 33 billion gallons a day were freshwater. Thus, from 2005 to 2010 freshwater use fell 6% in California. In both 2005 and 2010, about 74% of all fresh water withdrawals were for irrigation so most of the reduction in freshwater withdrawals was in irrigation allocations and probably an increase in water reuse in urban centers.

The 38 billion gallons per day (42,000,000 acre-feet per year) of withdrawals in 2010 were distributed among eight categories:

• Irrigation: 61% (23,000 million gallons per day, or 26,000,000 acre-feet per year).
• Thermoelectric power generation: 17% (6,600 million gallons per day, or 7,400,000 acre-feet per year). This water is saline and not usable for irrigation or consumption.
• Public supply: 17% (6,300 million gallons per day, or 7,100,000 acre-feet per year). Average daily gross per capita use was 181 gallons, this is very high individual use probably attributed to outdoor use- watering all those suburban lawns.
• Aquaculture: 3% (970 million gallons per day, or 1,100,000 acre-feet per year).
• Industrial:  1% (400 million gallons per day, or 450,000 acre-feet per year).
• Mining: 0.5% (270 million gallons per day, or 300,000 acre-feet per year).
• Livestock: 0.5% (190 million gallons per day, or 210,000 acre-feet per year).
• Self-supplied domestic use: < 0.5% (170 million gallons per day, or 190,000 acre-feet per year). Average daily per capita use was 69 gallons. This number is in line with per capita use in Virginia in 2005 and may only reflect that you do not water your lawn off your well. 

In California an arid state, average daily use of water by individuals on public supply is 181 gallons a day. This is more than two and a half times the per capita use for those on private wells and in places like Virginia. This use has to be for exterior water use, watering gardens and lawns. The watering restrictions in place for the current drought are attempting to address this area. However, in California 74% of fresh water is used for agricultural irrigation. Without irrigation, crops could never be grown in the arid and semi-arid lands of California where agriculture is a $45 billion dollar industry, subsidized by cheap water. Let’s hope that the USGS data can help California manage their water into the future.