It seems ironic. "Cloud" in its traditional meaning is something that delivers water. But when "cloud" means cloud computing, it does just the opposite. Computing in the cloud requires millions of servers running in thousands of data centers. These servers generate a lot of heat as they handle our email and other online services, but at the same time they need to be kept cool. That means data centers need massive cooling abilities, which requires water, and lots of it.

Some of the nation's biggest cloud providers, and providers of cloud-based services, are located in Silicon Valley--Google and Facebook, just to name two. California has about 800 data centers and all together they may be using more than 100 billion gallons of water a year. That's not great in a state that's struggling with the worst drought in 100 years. 

A few months ago, the Wall Street Journal called attention to this potentially destructive water usage, and others have jumped into the fray to decry Silicon Valley's water usage. "The tech industry is threatening to drink California dry," is how The Guardian put it. 

That kind of language is a little overblown. Though 100 billion gallons certainly seems impressive, it's about one tenth the amount of water in residential use for things like lawns and swimming pools, and less than a hundredth of the water used for California agriculture. Still, tech companies -- most of which pride themselves on being good environmental citizens -- need to learn to get by on less water, especially as cloud computing and cloud-supporting data centers continue their rapid growth. So the industry has turned its considerable ingenuity to reducing its contribution to the drought.

Here are some of the changes they're making or considering:

1. Turning down the AC.

This is probably the simplest change a cloud company can make, and it's been recommended by Amazon Web Services VP James Hamilton. Most data centers keep the temperature in the mid-70s, he says. That tallies with recommendations from the heating and cooling industry association, but also leads to more energy consumption and water usage than is needed. All servers on the market these days can run at 95 degrees with no ill effects, he says--so why are we keeping things so cool?

2. Building walls.

This is another suggestion from Hamilton and it makes perfect sense. The way most servers (and desktop computers) deal with heat is uniform: They suck in cool air from the front to cool their systems and then blow hot air out behind. Standard data center design takes advantage of this fact by setting servers back to back, creating cold aisles and hot aisles. 

Hamilton suggests taking this a step further and putting walls around the hot aisles so that air doesn't "leak" around the servers and back to the cold aisles. It doesn't matter if the hot aisles get very hot since the servers are blowing air into them, not pulling air from them, so the hot air won't reach delicate computer components.

3. Using recycled water.

Water that's been used before for something else and then recycled is one clear answer to California's drought. Various cloud companies and technology companies are working with local utilities to use recycled water in their data centers.

4. Making data centers more water-efficient.

If technology's needs are the problem, technology may also be part of the solution, and various companies are using data analysis to figure out how they can use less water. More data centers are tracking their water consumption closely, and the data center analysis platform Romonet recently added water tracking to its capabilities.

5. Moving elsewhere.

Can California companies locate their data centers in other places where cooler weather means less cooling is needed or water is more plentiful? Yes -- sort of. Facebook has done just that by opening one data center in Sweden and now planning another in Ireland.

But because cloud computing physically happens at a data center, if you move that data center too far away from customers, they will experience lags. Google, though, may have found the perfect solution by locating a major data center in The Dalles, Oregon, right on the bank of the Columbia River. Not only does that give them access to plenty of hydroelectric power, it also gives them all the water they need. They're only a state away from their headquarters and California customers, but they're not drawing on the state's dwindling water resources, or worsening the drought.