It's a bathroom, a planter, and a fertilizer all rolled into one.

While working on a class project, Eddie Gandelman wondered if the public restroom could be made a more comfortable, welcoming space.

"I think the urinal in public restrooms is one of the worst designed things," says Gandelman, a 22-year-old design student at the University of Cincinnati. He sought to brighten the space by adding plants. Then the light-bulb went off. "I was looking at my sketches and thought, 'Hey, that would be kind of cool if you could water the plants with your pee,'" Gandelman recalls of his ah-ha moment last spring. “I researched it and found that it could work.”

The result is When Nature Calls, a urinal that filters the sodium and acidity from urine via a three-step process involving activated charcoal, crushed limestone and greensand, then uses the end product to water plants.

It quickly attracted attention. Stories appeared last summer on popular technology and design sites and as far afield as the U.K., highlighting the concept's simple ingenuity and conservation of water and the environment. Feeling left out, many women asked Gandelman about a toilet version (not yet).

The concept of separating solid waste from liquid waste to use either or both as fertilizer is not new. Some 135,000 urine-diversion toilets are used in Sweden, where some of the collected urine is passed on to farmers. Some farmers in developing regions of China and other countries do the same.

But the concept has never been brought to the urinal, and the filtering and plant watering have never been so immediate – or timely. In recent weeks, Gandelman has been fielding calls from architects looking to incorporate his idea into their latest sustainable building designs.

Yet no prototype has been built; When Nature Calls exists only on paper. Gandelman recently spoke with an engineer and learned that the concept, as currently designed, would be very costly and difficult to develop. “My next step may be finding the right people with the right skills to take it to the next level,” he says.

A writer at Trend Hunter suggests restaurants use them to grow fruit and vegetables, cutting costs and carbon emissions simultaneously. Another possibility is installing the urinals in a public restroom in a city park. But rather than water plants directly attached to the urinal itself, as in the rendering, the filtered urine could be directed outside, to water, say, a flower bed.

“That would be a good and logical next step for it to go,” says Gandelman, who expects to graduate next month. “The plants could have a sign: 'This is being watered by urine.'”

Hopefully such a sign wouldn't inspire tipsy, full-bladdered bypassers to contribute to the cause.

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