The South African city of Durban is looking to buy liquid waste to encourage residents to use dry toilets. Aiming to improve hygiene and save money, the port city has installed in home gardens about 90,000 toilets that don’t use a single drop of water. Now Durban wants to install 20-litre containers on 500 of the toilets to capture urine rich in nitrates, phosphorus and potassium which can be turned into fertilisers.