November 5, 2009
The American population is getting more efficient at using our water supply. We used 410 billion gallons of water per day in 2005, according to new estimates from the U.S. Geological Survey, and this hasn’t changed much since the USGS first started reporting on the topic in 1950, despite a 30 percent increase in population since then.
It’s where our water goes that made me blink: 49 percent is used in the production of electricity and another 31 percent for irrigation in agriculture. The stuff we drink and wash our clothes in and water our lawns with is only a small percentage. The irrigation number isn’t too shocking as agriculture is a huge industry in this country. But I had no idea we were using so much water to turn on our lights. The USGS explains:
Water for thermoelectric power is used in generating electricity with steam-driven turbine generators….Cooling-system type is the primary determinant for the amount of consumptive use relative to withdrawals. Once-through (also known as open-loop) cooling refers to cooling systems in which water is withdrawn from a source, circulated through heat exchangers, and then returned to a surface-water body. Large amounts of water are needed for once-through cooling…Recirculation (also known as closed-loop) cooling refers to cooling systems in which water is withdrawn from a source, circulated through heat exchangers, cooled using ponds or towers, and then recirculated. Subsequent water withdrawals for a recirculation system are used to replace water lost to evaporation, blowdown, drift, and leakage. Smaller amounts of water are withdrawn for recirculation cooling than for once-through cooling.
The amount of our water that goes to power generation has increased over the last 20 years. The industry as a whole has become more efficient in its water use (the average amount of water used in the production of a kilowatt-hour of electricity has declined since 1950), but that is because there are more power plants that use recirculation cooling in which the water is used over and over.
Climate change is likely to change our available water supply over the next century. Greater efficiency can only help in the management of this resource, especially if it becomes more scarce. I’ll make no recommendations about how to change our water management, but just looking at the chart above gives me some ideas about where we should target our efforts.
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