Why cities need a system for collecting water?

There is always a shortage of water in Cities. As the population is increasing, the need of water is also increasing. One of the ways of  increasing the availability of water is to collect rainwater and store it for later use. Collecting rainwater in this way is called rainwater harvesting.

There are two main techniques of rainwater harvesting, and they are- 

1. Rooftop rainwater harvesting- The rainwater is collected from the rooftop to a storage tank, through pipes. This water may contain soil from the roof and needs filtering before it is used. Instead of collecting rainwater in the tank, the pipes can go directly into a pit in the ground. This then seeps into the soil to recharge or refill the groundwater.

2. Another way of Rainwater harvesting is to allow water to go into the ground directly from the roadside drains that collects rainwater.