Last week, we covered one of the talks from a great session on using waste as a resource that took place at the annual meeting of the American Association of the Advancement of Science (AAAS). That one was about using farmyard byproducts to generate biogas, but it wasn't the only example of increasing energy efficiency through capturing waste. David Scott gave a presentation on how Abu Dhabi is meeting its fresh water needs using waste heat from power generation, and it's a strategy that might come in handy here in the US in the not-too-distant future.

One of the Gulf states, Abu Dhabi has lots of natural gas and plenty of spare heat, with some of the hottest temperatures recorded on our planet during their summer. As a result, the thermal efficiency of its gas turbine plants, even when run on a combined cycle (where waste heat powers a secondary steam generator) is only about 41 percent, compared to up to 60 percent in more temperate climates. So far, not so good.

But while Abu Dhabi has lots of gas and lots of heat, it doesn't have a lot of fresh water. With 1.7 million people and a need for around 240 million gallons of fresh water a year, that means desalination. Removing salt from sea water requires a fair amount of energy, with the easiest method being flash distillation; you use heat to turn the water into steam, leaving the salt behind. By using the waste heat of their gas turbines to desalinate sea water, Abu Dhabi is able to turn that 43 percent efficiency into more than 90 percent efficiency, which is fairly impressive by anyone's standards.

It's not all gravy though. They can reach peak efficiency of 91 percent, but that's subject to seasonal demand. Abu Dhabi's power needs are a lot greater in the summer, when everyone is running air conditioning, than in the winter. February's energy needs are only a third of those in the middle of summer—with such low generation, the combined generation and desalination process becomes much less efficient. If winter demand for power is low enough, there often isn't enough heat around for desalinization.

It might not be too long before we need to start considering strategies like these here in the US. The southwestern part of the nation has a rapidly growing population, and that means rapidly growing water needs. Much of that water currently comes from the Colorado river, which is almost completely dry by the time it reaches the Pacific. In the 1930s, the various states that take water from the Colorado split up the rights, but overestimated the amount of available water by more than 40 percent, and that was before the population and agricultural activity skyrocketed.

Will large-scale desalination become necessary for California and Arizona in the coming years? Climate change is predicted to exacerbate things, so Abu Dhabi's strategy might prove effective, although as we reported last year, some academics think we may be able to respond to the problem without adopting such measures.

Still, it would behoove the states to start thinking about how to deal with the coming problem. California supplies an enormous proportion of the country's food, and nearly 80 percent of its water is used for agriculture. Building in the capacity to desalinate before we reach a crisis point will be cheaper than responding to a crisis.