Energy And Water 2: The Thirsty House

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Water use per person per day. National Renewable Energy Laboratories.

Of course you need water to wash your clothes, but did you know that you also need water—indirectly—to power your washing machine?

And it also takes water to run your laptop, your dishwasher and to keep your lights on.

That’s because it takes water to create energy. The electricity sector uses 143 billion gallons of freshwater a day to run power plants.  Coal plants typically use 20 to 50 gallons of water to produce one kilowatt-hour of electricity. And that doesn’t even take into account the water needed to mine the coal and store the coal waste.

So how much water does it take—indirectly—to power your washing machine?

According to this report by The Union of Concerned Scientists, the math looks a little like this:

  • It takes .25 kWh of energy to run the washing machine’s motor
  • It takes 7 kWh of energy to heat 40 gallons of water from 10°C to 46°C.

So to run a load takes approximately 7.25 kWh of electricity. And how much water is needed to produce that amount of electricity? That depends on what type of power plant it is, and what technology it uses.  But here are the lower and higher estimates:

  • A power plant using 20 gallons of water for each kilowatt-hour produced would require 145 gallons of water to produce 7.25 kWh.
  • A power plant using 60 gallons per kWh would require 435 gallons of water.

By these calculations it could take between three and ten times the amount of water to power the washing machine as it takes to actually clean the clothes. And that is just the water required to run one electrical appliance.

So it is no surprise then that that household water use for energy far exceeds household water used for washing, cleaning, drinking etc.

With the average person using 100 gallons of water per day for direct use, the average household of four uses 400 gallons in indirect use. Figure 2 shows that the average household can indirectly use from 600 to 1,800 gallons of water to meet their electricity needs.

Figure 2: Average daily water use by a U.S. Family of Four.  Union of Concerned Scientists.

Figure 2: Average daily water use by a U.S. Family of Four. Union of Concerned Scientists.