What is groundwater anyway and why are people talking about it? Basically, groundwater is fresh water stored underground. The underground layer of water-bearing permeable rock from which groundwater can be extracted using a well is referred to as an aquifer. Think of it as an underground lake. Aquifers vary, based on geology, but all are filled through the infiltration of rainwater and surface water flowing through the soil. In this way, groundwater and surface water in a given area are simply parts of the same overall water supply (Figure 1). The water sinks down into the soil and joins its watery brethren in a dark, sweet underground reservoir. Aquifers tend to have exceptional water quality as the roots, soil, and geology cleanse the water during its downward, gravity-driven journey of infiltration.
What is distinctive about groundwater supplies in areas with large aquifers is that they can store very large amounts of fresh water accumulated over hundreds to even thousands of years (Figure 2). As a result, groundwater has the potential to offer significant reserves for a region experiencing a prolonged period of diminished rainfall and drought. This remains true as long as the groundwater supplies are replenished during wet years.
From early in California’s development, groundwater has been the water source to turn to during times of drought when surface water sources diminished or dried up entirely. The drought of 1880 was the first major impetus for groundwater development in the Central Valley. However, through the 20th century a water “market” developed in California that incentivized the delivery and sale of as much water as possible in any given year. While surface water began to be regulated in 1914, groundwater was not, and this led to the greatest number of and deepest wells possible. By the 1960s and ’70s withdrawals greatly exceeded recharge, causing widespread land subsidence in the western and southern San Joaquin Valley, as much as 28 feet near Mendota, CA.
Following a generally wetter than average period that lasted into the 21st century, California is now deep into the most severe drought on historical record. In an average year, 39% of the water consumed in the state comes from groundwater. Three years into this drought, that number is up to 60% and could reach 65%, according to a recent California Water Foundation report. Eighty percent of the state’s freshwater is used for agriculture, primarily in the Central Valley. The Central Valley’s reserves are shrinking by 800 billion gallons a year—enough to supply every resident of California with water for seven months, according to Jay Famiglietti, director of the University of California Center for Hydrologic Modeling. “The ability of people to keep drilling was the equivalent of deficit spending,” said Lester Snow, former head of the DWR and Executive Director of the CA Water Foundation. As the drought continues, each gallon of freshwater in California becomes increasingly valuable in the California water market. In a context where farmers and cities who tap underground aquifers are allowed to pump as much water as they want while surface water rights are strictly regulated, the system is easily exploited by greedy individuals.
The Modesto Bee reported in May of this year on one example-the proposed sale by two landowners of $46 million in water pumped from 13 Merced County wells to Stanislaus County-based water districts. This sale has since been scaled back, but the extreme nature of this sale no doubt provided impetus for the passage of a historic measure that regulates groundwater for the first time in state history, making California the last Western state to place controls on the amount of water taken from wells.
The bill, signed by Governor Brown on September 16, requires local government officials to bring all “high” or “medium” priority groundwater basins up to sustainable levels by 2040. The bill intends to limit overpumping by directing local agencies to construct their own “groundwater sustainability plans,” with fines for violations. There are also provisions for the state to usurp local plans if those plans continue to result in groundwater depletions after 2025.
It is fair to celebrate this long overdue general accounting of groundwater use and supplies in California. It is important to remember that freshwater is a part of the public trust. Measures like this are simply the very beginning of an overall suite of reforms to California water management that are needed to share this most precious and essential resource more equitably, efficiently, and intelligently, constituting the only path toward an economically and environmentally resilient future.