In the QoD, you mentioned that Nevada has water "banked" in the aquifer and, I believe, in return-flow credits from recycling water back into Lake Mead. Is that true? And if so, how much water is in the savings account? How long might it last in a serious crisis?
In the previous QoD about where our water comes from, we wrote that southern Nevada returns almost all of the water that's drained into sewers back to the lake, after being treated, in exchange for return-flow credits, from which its total allotment of lake water is subtracted. So even though Nevada is entitled to 300,000 acre-feet of Mead and used around 475,000 annually over the past few years, the net use, minus the credits, was only 223,000 acre-feet, right around 75% of its allotment.
Most of the excess water, which currently adds up to 2.2 million acre-feet, is banked in Lake Mead, almost a million acre-feet. The rest is stored underground: in the aquifer underlying southern Nevada, in Arizona via the Arizona Water Banking Authority, and in California via a number of different agreements.
From all that surplus, the Southern Nevada Water Authority can draw up 90,000 acre-feet annually. But it leaves all the water in the bank. It's not, and can't be, used to support or sustain development. It's for crisis management only. Which is why the Water Authority continues to place so much emphasis on conservation.
At the current usage rate of 475,000 acre-feet per year, excluding return credits, if the banked water has to be used in a severe crisis, 2.2 million acre-feet is the equivalent of four to five years of water. In other words, not much. But better than nothing.
