Water heating in schools may be done by using electric, gas or solar water heaters. In general practice a gas or electric water heater is usually close to the taps that it is connected to. They might be either located hidden away in cupboards or situated outdoors. Solar water heaters are mounted on the schools roofs, having the storage tank located. These heaters are highly energy efficient as they use solar energy, which is free, and do not produce any harmful green house gases in the process.