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It’s not really possible for a human being to imagine a trillion gallons of water. So here are some analogies:

* It’s 9 percent of the total water needed to end the California drought, according to NASA (which reported in December that the state has a water deficit of 11 trillion gallons).

* It’s about 40 million swimming pools and 24 billion baths.

* It’s about equal to the capacity of Florida’s vast Lake Okeechobee.

And amazingly, according to the Environmental Protection Agency, it may also be the amount of water that Americans needlessly waste, every year, because of leaky kitchen and bathroom faucets, malfunctioning toilets, errant sprinkler systems and much else. These leaks “can waste more than 1 trillion gallons annually nationwide. That’s equal to the annual household water use of more than 11 million homes,” the EPA said.  The agency gets the figure — which is at the center of its “Fix a Leak Week” campaign, running this week — by combining together data on home water use with population statistics.

How could we cluelessly waste such a vastness of water? “I think how it goes unnoticed is, people see a couple of drips coming out of their shower head, or sprinkler outside, or faucet, it doesn’t seem like that much,” said Karen Wirth, who does marketing and outreach for the EPA’s WaterSense program.

[Your shower is wasting huge amounts of energy and water. Here’s what you can do about it]

Leaky pipes notwithstanding, much of the problem is hardly invisible. Rather, it comes from things we’re all aware of, like leaking faucets. A simple tool from the U.S. Geological Survey allows you to calculate how much water these can waste, showing that one faucet leaking one drip per minute adds up to 34 gallons per year — so you can begin to see how this adds up. The number for 1 million homes with a single faucet leaking at this rate, meanwhile, would be more than 34 million gallons. And of course many leaks drip much more than once per minute — and many homes have more than one leaky faucet.

And then there are our toilets, which are, if anything, an even bigger problem. Many are losing water, or even constantly running, because of problems like worn out flapper valves, which steadily allow water to dribble from the tank into the bowl. “A continuously running toilet can waste between 1,000 and 4,000 gallons of water per day and potentially increase your bill by hundreds and even thousands of dollars,” notes the Arlington, Va. county water page.

“There’s simple ways to check your toilet. Just put a few drops of food coloring in the tank. If that shows up in the bowl, you have a leak,” Wirth said.

Outdoor irrigation systems are another problem area. Because of the American obsession with green, tall standing turf grass, we install underground sprinkler systems and run them regularly, and often don’t notice when they leak. “An irrigation system that has a leak 1/32nd of an inch in diameter (about the thickness of a dime) can waste about 6,300 gallons of water per month,” noted the EPA.

[Americans are judging their neighbors’ lawns — with surprising environmental consequences]

Other areas of potential water loss include leaking pipes, outdoor hoses, and connection lines to clothes and dishwashers.

Wasted water comes with a cost. The city of Daytona Beach, Fla., estimates that a faucet leaking 10 drips every minute wastes 526 gallons of water per year, adding up to $10.91. Clearly, a running toilet can waste much more — and cost much more — than that. The EPA estimates that about 10 percent of water bills across the country could be reduced by addressing leaks.

The agency recommends not only fixing leaky faucets and toilets (of course) but running a home water leakage test. It’s really simple: Look at your water meter just after leaving your home (with all water using fixtures and devices turned off) and then upon returning. And see if it has moved.

“I think what people don’t understand is what the magnitude of the compounded problem is,” Wirth said .