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Where the water flows

Santiago Miret, Ph.D. student, materials science & engineering | February 18, 2014

California is currently experiencing a historic drought, one of the worst the state has had in over 100 years. The large amount of news coverage about the drought has instilled the notions water usage and water efficiency in the minds of regular consumers. Yet, when taking a closer look at where water is really flowing, it becomes evident that consumers may have the most impact on their water efficiency by actually increasing their energy efficiency.

UC Berkeley recently announced an effort to increase campus water efficiency and reduce campus water usage. The following graph from the Environmental Protection Agency (EPA) outlines water usage from different sources in an average household:

Household Water Consumption – Source: EPA

As seen from the chart above, the most direct ways to reduce water consumption in the home is to fix all leaks and to be conservative about shower and toilet usage. Yet, when looking at the larger picture of the water system, it becomes evident that residential water usage is dwarfed by water usage in agriculture and energy generation.

Water Withdrawals Over Time – US Geological Survey

The data from the US Geological Survey (USGS) shows residences (approximated by “Public Supply”) withdraw less than a third of the water of irrigation and less than a quarter of the water needed to generate thermoelectric power, which is the basis of today’s energy system. The large amount of water required for thermoelectric power generation stems from the fact that most of today’s energy is produced by steam turbines, which require vast amounts of water to operate.

The schematic above illustrates how critical water is for operating a steam turbine. Initially, water is fed into the boiler and turned into steam by burning fuel. The steam then turns the turbine, which is connected to a generator that produces electricity. Water is then also used to cool the steam after it has passed through the turbine, and recycled throughout the system.

Given that irrigation and thermoelectric power generation dominate, it may appear that the regular consumer can do very little to actually improve overall water efficiency. If one were to look solely at reducing the domestic water usage, then that may be the case, yet consumers can indirectly affect water efficiency by improving their household energy use. Given that power generation takes up more than 4x water than households, a saving in energy would have a 4x larger impact on water reduction than trying to save water from household sources.

In addition to increasing household energy efficiency, switching to renewable power source would have an even more profound impact on water reduction. The vast amounts of water required to generate electricity from thermoelectric sources stems from the integral part the water plays in operating the steam turbine system. Yet, renewable energy sources, such as wind and solar, do not require water to produce energy during their operation. A grid with more renewable energy sources, particularly wind and solar, would increase both the carbon and water efficiency of the area it serves.

The second major contribution to water usage is irrigation required for agriculture. A study by the Pacific Institute investigated the water content of some everyday items. If you are trying to be more water conscious, you might consider thinking of your water footprint next time you consume one the following common items. The full list is available here, but here are some highlights that I found particularly interesting:

  • A glass of tap water costs 1 gallon of water per gallon, as expected, but bottled water can cost ~3 to 4 gallon of water
  • A cup of coffee costs ~280 gallons of water, a cup of tea costs ~30 gallons
  • A glass of beer costs ~75 gallons of water
  • A pound of hamburgers cost ~2,100 gallons of water
  • A pound of apples cost ~90 gallons of water, a pound of corn ~120 gallons, and a pound of sugar ~190 gallons
  • A pound of chicken costs between 400 to 700 gallons of water; a pound of beef costs between 2,000 and 9,000 gallons of water

Cross-posted from BERC Blog, published online by the Berkeley Energy & Resources Exchange, a network of UC Berkeley scholars and industry professionals.