The beets Surendra Pradhan and Helvi Heinonen-Tanski grew were perfectly lovely: round and hefty; with their skin a rich burgundy; their flavor sweet and faintly earthy, like the dirt from which they came. Unless someone told you, you’d never know the beets were fertilized with human urine.

Pradhan and Heinonen-Tanski, environmental scientists at the University of Kuopio in Finland, grew the beets as an experiment in sustainable fertilization. They nourished the root vegetables with a combination of urine and wood ash, which they found worked as well as traditional mineral fertilizer.

“It is totally possible to use human urine as a fertilizer instead of industrial fertilizer,” says Heinonen-Tanski, whose research group has also used urine to cultivate cucumbers, cabbage and tomatoes. Recycling urine as fertilizer could not only make agriculture and wastewater treatment more sustainable in industrialized countries, the researchers say, but also bolster food production and improve sanitation in developing countries.

Urine is chock full of nitrogen, potassium and phosphorus, which are the nutrients plants need to thrive-and the main ingredients in common mineral fertilizers. There is, of course, a steady supply of this man-made plant food: an adult on a typical Western diet urinates about 500 liters a year, enough to fill three standard bathtubs. And despite the gross-out potential, urine is practically sterile when it leaves the body, Heinonen-Tanski pointed out. Unlike feces, which can carry bacteria like salmonella and E. coli, urine poses no health risks-astronauts on the International Space Station even drink the stuff-after it’s purified.