A new calculator reminds us that every bite of food, every mile we drive, and every light switch we flip relies on the wet stuff.

Many of us are only dimly aware of how much water we use throughout the day. Last year, an Indiana University survey asked more than one thousand Americans to estimate the amount of water it takes to flush the toilet, wash clothes, and other kinds of normal household uses. On average, participants underestimated their use by a full factor of two.

And those were only the most obvious kinds of water-sucks. In the developed world, every bite of food, every mile we drive, every light switch we flip relies on the wet stuff. All of that "virtual" water use—the kind you don't see—is where you get estimates like this: The average American has a "water footprint" of 2,220 gallons per day.

That number—which is likely way higher than most you've probably seen before—comes from a new water footprint calculator from Grace Communications Foundation, an organization that promotes public awareness about sustainability issues. Embedded above, the calculator probes broader and deeper than past iterations have, using national data and behavioral studies to average the number of gallons per day associated with your energy and fuel consumption, shopping habits, recycling habits, meal choices, and even pet food purchases, on top of normal household uses.

I average 1,459 gallons per day, which is well below the national average, but still startlingly high. That score comes with links to tips about how to save—mostly obvious stuff, like buying efficient washing machines and taking shorter showers, but also suggestions like eating less meat and shopping at thrift stores, since animals and cotton are so water-consumptive.

But when you start to consider ways to shrink your water footprint, it's important to remember the difference between water withdrawal and water consumption. Power plants, for example, rely on incredible amounts of water to run. But the water that gets used to create energy is mainly being diverted from its source; it goes back into the ground or into streams and will be used again. That's different than water that is consumed, permanently, when it evaporates, turns into a food product, or a textile. The calculator largely reflects water consumption, but also includes questions about withdrawal.

"The numbers are pretty accurate," says Doug Parker, Director of the California Institute for Water Resources. "But my question is, what do you do with it? If I'm interested in solving the drought in California, using less energy from power plants doesn't really matter because that water can be used downstream by a farmer."

Then again, some water that gets used by power plants does evaporate, never to be used again.* And saving energy is helpful to the environment from a carbon-emissions standpoint. But Parker's point is well taken—your total water footprint doesn't necessarily imply you should look to to change all of your behaviors.

Maybe it's fair to say that best use of this calculator isn't so much the result, but the process: It forces you to consider every invisible gallon that makes waking life possible in the developed world.

*This article has been updated to clarify how the calculator measures energy-related water use.

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