Actually, it's (literally) a cool technology idea for developing countries:
The engineering students at the University of Cape Town (UCT) have been harvesting urine from men's toilets.
After first making a solid fertiliser, the leftover liquid is then used in a biological process "to grow" what the university calls "bio-bricks".
The process is called microbial carbonate precipitation.
The bacteria produces an enzyme that breaks down urea in the urine, forming calcium carbonate, which then binds the sand into rock hard, grey bricks.The advantage:
Normal bricks need to be baked in high-temperature kilns that produce large amounts of carbon dioxide.