Due to the lack of water people were forced to use rainwater. Mercury from coal burning buildings, bird faeces etc may destroy the rain water. So we cannot use it. Also some rooftop material may demolish rain water and that may be very harmful to human health. After purification of rain water you could use it as drinking water. Otherwise it can be used for flushing toilets, washing clothes, watering the garden, washing cars etc. The method to store rainwater for reuse before it reaches the aquifer is called rainwater harvesting. Storage of rainwater on surface for future use and recharge to ground water are the main two methods for rain water harvestings. Cochin flats apply many techniques or method to purify rainwater and it used as drinking water. The methods or technique to purifying rainwater includes chemical purification, solar pasteurization, boiling etc.