Sustainable sanitation is a type of sanitation system which was first defined by members of the Sustainable Sanitation Alliance. To be sustainable, the sanitation system should meet the following five criteria: it should be economically viable, socially acceptable, technically and institutionally appropriate, and protective of the environment and the natural resources. The purpose of sustainable sanitation, like sanitation in general, is to protect and promote human health by providing a clean environment that reduces disease, particularly by transmission via the fecal-oral route. Sustainable sanitation, defined in this way, may or may not have an emphasis on reuse of excreta.