The European Space Agency says human urine could one day become a useful ingredient in making concrete to build on the moon. The agency said researchers in a recent study found that urea, the main organic compound in urine, would make the mixture for a “lunar concrete” more malleable before it hardens into its sturdy final form. It noted that using only materials available on site for a moon base or other construction would reduce the need to launch supplies from Earth. The main ingredient in “lunar concrete” would be a powdery soil found on the moon’s surface. ESA said urea would limit the amount of water necessary in the recipe. “Thanks to future lunar inhabitants, the 1.5 liters of liquid waste a person generates each day could become a promising by-product for space exploration,” it said in a statement. On Earth, urea is used as an industrial fertilizer and raw material by chemical and medical companies.