The Southern Nevada Water Authority’s board will take up a proposal this Thursday to ship 150,000 acre feet of Las Vegas’s unused Colorado River water to Southern California to help out during California’s epic drought.

Hoover Dam, Lake Mead bathtub ring, February 23, 2015. Elevation 1088.97

The water will help the Metropolitan Water District of Southern California make up for shortfalls in its supplies from Northern California, where drought has dramatically reduced the amount of water available for shipment through California’s State Water Project. Met is basically desperate, and Las Vegas has been so successful at water conservation that it is only using 75 percent of its Colorado River allocation these days.

If I was trying to explain this in the simplest possible terms, I would put it this way: Las Vegas is selling L.A. and San Diego 150,000 acre feet of water at a price tag of $295.83 cents per acre foot. But language here matters, so let’s be careful about the legal terminology. It would be wrong to call this a “sale” of water. More like a loan, or a banking agreement? The agreement between SNWA and MWD calls for Met to pay Vegas $44.375 million, and Vegas in turn will “store” 150,000 acre feet of water in Met’s system, that might be paid back (water and money) some day maybe sorta. But “store” really means Met can just use it to meet drought needs now.

Storage and Interstate Release Agreement

This is made possible by a “Storage and Interstate Release Agreement“, which provides the states of the Lower Colorado River Basin the flexibility to do water deals across state lines without calling them water transfers. Met and Southern Nevada have had such an agreement in place since 2004, and Southern Nevada already has 205,225 acre feet of water “stored” in Met’s system. (Nevada has another 601,041 acre feet stored in Arizona.)

Matt Jenkins in his High Country News profile of Pat Mulroy earlier this year had a great bit of business explaining the linguistic care with which these deals must be handled:

[T]ransfers, even within the Lower Basin, are … politically charged. “Don’t ever call it a transfer,” (Mulroy) scolded during a 2008 interview. “It’s a banking agreement. That thing will disappear on us tomorrow if we call it a transfer.”

So this is definitely not a transfer. If and when Las Vegas needs the water back, it’ll pay Met “a proportional amount of its costs” and grab the water from Lake Mead via an accounting swap. (It’s not like it makes sense to literally pump the water back uphill from Diamond Valley Lake to Vegas.) So maybe this is more like a “loan” of water?

Whatever we call it, it’s an important example of the sort of adaptive capacity Colorado River water managers have been developing in recent years to overcome the legal strictures that tie up water management flexibility under the cumbersome Law of the River.