Eco-friendly public toilet in India. This toilet can be connected in three ways. The first is to the classic sewer system. The second is to an on-site treatment system, which uses anaerobic treatment. The third is to a Caltech reactor developed with the help of the Bill and Melinda Gates Foundation. Many developing countries lack the toilet facilities found in developed countries. Research is aimed at developing sustainable toilets in such locations that also minimise the environmental impact on water usage. Photographed in 2019.