- Groundwater is a vital component of California’s water supply.
Hidden underground, groundwater typically accounts for about 35% of the water used by California’s farms and cities—in some regions the share is larger. Some communities rely entirely on groundwater for their drinking water. In dry years, groundwater becomes even more important as pumping increases to make up for the lack of rain.
SOURCE: Department of Water Resources.
NOTES: The figure shows total groundwater pumping, excluding active groundwater recharge (1–11% of total pumping, depending on the year). Precipitation is measured by the Sacramento Valley Water Year Index, which accounts for water in storage from the previous year.
- California’s minimal groundwater regulation has encouraged over-pumping.
In contrast to surface water, groundwater use has largely been unregulated under California law until recently. This regulatory gap has encouraged excessive pumping—or overdraft—in some areas. It also causes problems for users of surface water because groundwater and surface water are often interconnected. Groundwater basins are naturally replenished by rainfall, stream flow, and irrigation water. As pumping causes groundwater levels to drop, basins draw in water from adjacent rivers and streams, reducing river flows and harming aquatic habitat.
- Many groundwater basins are being used unsustainably.
In some basins (especially those in major agricultural regions in the southern Central Valley and Central Coast), groundwater withdrawal exceeds the amount that can be replenished. On average, California’s agricultural and urban sectors use about 42 million acre-feet of water per year, of which one to two million acre-feet comes from excess pumping of groundwater. Declines in groundwater levels have serious repercussions, including higher energy costs to pump water from deeper wells, sinking lands (which can damage vital infrastructure such as canals and roads), and reduced water quality (especially in coastal aquifers, which draw in seawater). During the current drought, some wells have gone dry, and the pace of well drilling has increased as farmers and communities look for new sources of water.
- Groundwater contamination is a growing problem.
Groundwater quality is a serious issue in some basins. In many rural areas, nitrate—produced by nitrogen fertilizer and manure—is polluting local drinking water supplies. Salinity is also damaging crops. In some urban areas, basins are contaminated by industrial chemicals. Treatment to remove contaminants from drinking water is costly, especially for small rural systems. Efforts are under way to reduce future contamination by controlling industrial discharges and changing farming practices, but some already-polluted basins need to be cleaned up.
- Better groundwater management would help California cope with droughts.
California’s groundwater basins can store large volumes of water, which is especially valuable during droughts. But pumping needs to be limited in normal and wet years so that groundwater levels can recover. Groundwater storage can be increased by spreading water on fields to percolate through the soil or injecting water into wells. Some urban areas—including much of Southern California and Silicon Valley—have created local authorities that can charge fees to fund recharge programs and regulate pumping.
- Promising reforms have recently been enacted.
In September 2014 Governor Brown signed the Sustainable Groundwater Management Act—legislation that gives local agencies the tools and authority they need to develop and implement sustainable groundwater management plans. The most stressed basins have until 2020 to adopt groundwater plans and until 2040 to achieve sustainability, and other basins have slightly longer to comply. The state will step in if agencies fail to act.
SOURCE: Department of Water Resources.
NOTES: The table shows total groundwater pumping as a share of total applied water use in the agricultural and urban sectors from 1998–2010, excluding active groundwater recharge. The wet and dry years show the minimum and maximum shares of groundwater. Total statewide use is based on statewide values and does not equal the sum of the regions.
SOURCES: Department of Water Resources (water use data, all numbers are for 1998–2010); State Water Resources Control Board (water quality).