I've been thinking a lot recently about water issues (which may or may not be related to work). There's been a lot of talk recently about an emerging "Energy-Water Nexus" that threatens future economic growth in the United States. Essentially, it follows from the observation that water supply and energy supply are largely interdependent. This makes a good deal of sense. Thermal electric power generation uses huge amounts of water, for example, to reject heat to the environment at the lower end of the thermodynamic cycle. Vast quantities of water are required for coal mining, gas extraction, and oil production. In turn, surface water and groundwater must be transported or extracted, and saltwater desalinated, for use in industry or in the home.
At first glance, this doesn't seem to be a problem - not particularly at least. After all, the volumes of water we extract have a far lower energy intensity than the water intensity of energy. Four things speak against that simplistic viewpoint - one of them an emerging trend.
First and foremost, the amount of water used in industry faces some pretty stiff competition. More than 70% of the water used worldwide is used in agriculture. Globally, industrial uses - including thermal power generation - account for maybe 16%. This might seem obvious, but for all the energy we expend on purifying and extracting water, only a little bit is going back to extracting and producing more energy.
Second, the amount of water we use is increasing, and pressure is being put on the energy side of things. With population growth comes increased water consumption. That much is obvious; what is less obvious are the first order effects on agriculture. Furthermore, with economic growth, power consumption and thus water devoted to power consumption rises linearly. To put that in perspective, we can compare the global statistics I cited above to the ones for the United States: Fully 53% of our water is used in industry, of which a whopping 49% (that's about 92.5% of what's used in industry as a whole) devoted to power generation. With economic growth in China and India, and soon Africa, starting, water stress suddenly is a whole lot closer to reality.
Third, all water issues are, with rare exception, local issues. Water isn't evenly distributed, and the weight of water makes it difficult to transport, so local areas must find their own solutions to water issues. Some places are already running short of water resources for industry. Two big examples are the middle Yellow River region in China and the Jamnagar industrial district in Gujarat, India. In the former, rampant industrial overinvestment has lead to water-guzzling factories being shut down and heavy rationing instituted. In the latter, overreliance (no pun intended*) on groundwater has caused water tables to fall to dangerously low levels - farmers outside the area have to drill 30ft deeper wells every year, and what they get is increasingly saline because of contamination from seawater.
Fourth, the emerging trend is even more water intensity in our energy consumption, with the rise of biofuels and biochemicals. Irrespective of subsidies, the economics of high oil prices have driven the adoption of these new technologies, almost all of which are water intensive. Consider that the processing of one gallon of corn ethanol requires 30 gallons of water consumed in the most advanced plant in the United States. A more typical case is 300-600 gallons.
So there's a darned good reason that a lot of the power and chemical process industry is starting to care about water issues again.
* The megacomplex of refinery and chemical plants in Jamnagar is owned by Reliance Heavy Industries. Yeah, probably no one got that.