There are seven states in the western part of the U.S. that rely heavily on the Colorado River basin as a valuable water source. However, a new study finds that these states are now drawing more water from groundwater supplies than previously predicted.
Roughly 400 billion gallons of water are used in the U.S. every day. Groundwater accounts for an estimated 95% of the nation’s fresh water resources, and roughly 40% of the people in this country rely on it as drinking water.
The river basin covers Wyoming, Colorado, Utah, New Mexico, Nevada, Arizona, and California, and it has lost about 65 cubic kilometers of fresh water over the past nine years, a startling finding to an already growing freshwater depletion problem. To understand the amount of water, this is nearly twice the volume of Lake Mead, the country’s largest reservoir.
According to NASA weather satellites which were used to investigate groundwater supplies in the area, roughly two-thirds of the water lost during these past nine years came from underground water supplies — not surface water. Groundwater is found in small pockets within the earth and is extracted and purified using various remediation methods.
“We were shocked to see how much water was actually depleted underground,” said Stephanie Castle, a water specialist at the University of California at Irvine and the lead author of the report.
The Colorado River Basin’s groundwater is regulated on the state level, not on the federal level, which makes it difficult to set bars on how much water is being used. California for example has no groundwater management rules, while Arizona has decided on underground aquifers to transfer surface water for later use.
Most years, all of the water from the Colorado River is pumped out of it before it empties into the Gulf of California, yet it still flows due to groundwater. In fact, scientists were shocked at the amount of groundwater that supplied the river. Some 2.78 trillion gallons of groundwater are estimated to exist for the entire planet, and this basin serves more than 40 million people alone.
Climate change and other environmental pressures due to booming populations in cities such as Denver, Phoenix, Los Angeles, and San Diego continue to be a major stress for water supplies. For example, water irrigation often pulls from groundwater, and this farming technique withdrawals roughly 128,000 million gallons of water per day.
As a result of unregulated groundwater usage, reservoir storage at Lake Mead won’t be enough to supply the region’s demand for fresh water, which will put even more pressure on groundwater supplies.
“We really don’t know how much water is down there. We’ve already depleted a lot of it. There could be more, but when we have to start to dig deeper to acces it, that’s a bad sign,” Castle said. “If [ground water basins] continue to be depleted, they don’t come back up.”
Groundwater doesn’t replenish as fast as surface water because it must seep into the earth, whereas surface water sources get their fresh water from rain and snow.