Rain in forests enters the ground and is stored; about 15% is gradually released and finds its way into natural streams. As it moves throught the soil it is filtered; this is why mountain streams are so clear.
Rain in cities falls on hard surfaces that carry dust and pollution from the atmosphere and animals. The water is not retained or filtered by the soil, and carries much of the pollution into the streams.
City folk can improve their streams and cities by slowing the release of storm water. By storing water in tanks, and using it to make lush green gardens and grow food, we can reduce “food miles”, improve our health, reduce the temperature of cities, reduce the requirement for airconditioning, reduce our energy bills, and reduce carbon.
Public policy has been to recommend the establishment of “drought resistant” gardens to reduce use of reticulated water. Rain water is the one natural resource we should use more.