Water is a precious resource and the document discusses rainwater harvesting. Rainfall is an important source of water but most rainwater is wasted, which could cause water problems in years with low rainfall. To save rainwater, rainwater harvesting collects and purifies rainwater so it can be used for days when river water is unavailable. Rainwater harvesting can be done at home or on a larger scale at schools, where very big tanks collect and purify rainwater.