In installing a new toilet there are a number of options to obtain the most water efficient model. A low flush toilet uses one to two gallons per flush. Traditionally, toilets use three to five gallons per flush. If an eighteen-liter per flush toilet is removed and a six-liter per flush toilet is put in its place, 70% of the water flushed will be saved while the overall indoor water use by will be reduced by 30%. It is possible to have a toilet that uses no water. A composting toilet treats human waste through composting and dehydration, producing a valuable soil additive. These toilets feature a two-compartment bowl to separate urine from feces. The urine can be collected or sold as fertilizer. The feces can be dried and bagged or composted. These toilets cost scarcely more than regularly installed toilets and do not require a sewer hookup. In addition to providing valuable fertilizer, these toilets are highly sustainable because they save sewage collection and treatment, as well as lessen agricultural costs and improve topsoil.