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Should We Use Recycled Rainwater to Flush Toilets?

Raindrops could help us to avoid squandering a precious resource.

You'll be shocked to hear this, perhaps, but the biggest single way that you use water in your household is to flush the toilet.

Older toilets use as much as 3.5 to 7 gallons per flush, and even the latest standard water-conserving models still use 1.6 gallons each time you do your business, according to the EPA. That accounts for about a quarter of your household use, on average.

There's a big problem with that, because we still cling to the practice, which dates back to 19th century municipal systems, of having one water supply pumped into the house. That means that we're flushing waste down the toilet with water that's been treated at considerable expense to be drinkable. And in places where water is scarce, it's an even bigger problem.

Future Cities Go Off the Water Grid

In drought-ravaged California, for example, the population has been flushing about 120 billion gallons per year. One water expert told the Los Angeles Times that high-efficiency toilets don't save as much water as expected, because people tend to flush them multiple times to get the job done.

But Drexel University engineers have a solution - at least, for cities where there is ample precipitation. Instead of using potable water in toilets, why not utilize rainwater collected from rooftops?

In a study just published in the journal Resources, the researchers report that it rains enough in Philadelphia, New York, Seattle and Chicago that if homeowners simply had a way to collect the water falling on their roofs, they could flush their toilets often without having to use potable water from municipal systems.

Video: How Much Water Do We Really Need to Drink?

"People have been catching and using rain water for ages, but it's only been in the last 20-30 years that we have realized that this is something that could be done systematically in certain urban areas to ease all different kinds of stresses on watersheds; potable water treatment and distribution systems; and urban drainage infrastructure," Franco Montalto, an associate professor in Drexel's College of Engineering, and director of its Sustainable Water Resource Engineering Lab,said in a press release.

The solution would also help eliminate another big problem - what to do with stormwater runoff in cities, which often picks up chemicals and refuse and contaminates the bodies of water into which the drains eventually empty.

What If California Runs Out of Water?

The team calculated that, with enough water storage capacity - a little more than a standard 1,000-gallon home storage tank - a three-person family in a home with the city's average roof size would have enough water to cover over 80 percent of its flushes throughout the year simply by diverting their downspouts to collect stormwater. With even bigger storage tanks, people might be able to virtually eliminate using potable water for flushing.

If you like this idea, offers a guide to installing a rainwater-supplied toilet.

A rainwater capture system like this could collect water to flush toilets.

It might sound a bit cramped, but there's an entire world of organisms that can call a drop of water their home. And, up close, they look practically out-of-this-world. Each year, the Nikon Small World competition sets out to collect some of the best microphotography. Take a look at some of this year's most stunning images of creatures that live in water. This photo from Dr. Jan Michels of Christian-Albrechts-Universität zu Kiel in Kiel, Germany shows Temora longicornis, a marine copepod, from its ventral view at 10 times magnification.

SEE MORE PHOTOS: It's a Nikon Small World After All

This microphotograph shows the diatom Melosira moniliformis at 320 times its size.

This algae biofilm photographed up-close makes what's usually referred to as "pond scum" look like art.

This Philodina roseola rotifer was alive and well when this microphotograph was taken.

This microphoto shows a water flea flanked by green algae.

NEWS: Tiny Flea Has More Genes Than You

Warfare in a water droplet! This microphoto shows a Hydra capturing a water flea at 40-times magnification.

NEWS: Ocean's Most Abundant Food Source Disappearing

One of the ultimate human pests -- the mosquito -- begins life as larvae, here shown suspended in a single droplet of water.

Ever wonder what sex between two freshwater ciliates looks like magnified at 630 times its actual size? Now you know!

This freshwater water flea is shown at 100 times its actual size.

Closterium lunula, a kind of green alga, is shown here. This particular specimen came from a bog pond, according to the photographer.

While it may resemble a visitor from outer space, this is what a zebrafish embryo looks like under a microscope, three days after being fertilized.

This microscopic crustacean appears yellowish-orange because it is mounted in Canada Balsam with crystals and other artifacts.

A white-spotted bamboo shark's embryonic pectoral fin makes for a stunning image under a microscope.

SEE MORE PHOTOS: It's a Nikon Small World After All