Human urine has been used to create environmentally friendly bricks by university students in South Africa.
They combined urine with sand and bacteria in a process that allows the bricks to solidify at room temperature.
"It's essentially the same way that coral is made in the ocean," said Dyllon Randall, supervisor at the University of Cape Town.
Normal bricks need to be baked in high-temperature kilns that produce large amounts of carbon dioxide.
'As hard as limestone'
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.
How many loo breaks to make a brick?
- On average a person typically produces between 200ml and 300ml of urine per urination
- A "bio-brick" needs between 25 litres and 30 litres to grow - this may sound a lot, but most of this urine is also used to produce about 1kg of fertiliser
- So to make one urine brick, you'd need to go to the loo about 100 times.
(These are all rough calculations from the bio-brick and fertiliser urine project.)
The strength and shape of the bio-bricks can be altered as required.
"When we first started this process last year, we achieved the same compressibility strength as a 40 per cent limestone brick," Dr Randall told the BBC Newsday programme.
"Just a few months later we've doubled that strength now just by changing the material we put into the mould and allowing the bacteria to cement the particles for longer - with zero heat, at room temperature."
Regular bricks are kiln-fired at temperatures around 1,400C (2,552F), according to the University of Cape Town.
But Dr Randal admits their process is much smellier, according to BBC report.
"Say you had a pet and it peed in the corner, and you have that strong smell - that's ammonia being released. This process produces ammonia as a by-product," he said, adding that this ammonia is then converted into nitrogen-rich fertiliser.