How to start rainwater harvesting in an existing building?

Currently a lot of existing buildings do not have systems through which they can harvest rainwater but can start doing so easily with a few simple steps.

Step 1: Identify a suitable catchment area 

• In most of the cases, the roof of an existing structure is best suited as a catchment area for rainwater harvesting.

Step 2: Estimate Rainwater Harvesting Potential

• Estimating the rainwater harvesting potential from the catchment area helps fashion and install a correct  storage or collection tank for the harvested rainfall.
• Formula to estimate Rainwater Harvesting Potential = Surface Area of catchment (sq. ft.) x Runoff Co-Efficient of Catchment Surface x Amount of Rainfall (mm)

Step 3: Select or Design Water Storage or Collection Tank

• It is difficult to select the correct size of a storage or collection tank in an existing building.
• Size of tank is affected by:
  • Available Space
  • Estimated Rainwater Harvesting Potential
  • Purpose of the harvested rainwater

Step 4: Connect existing Plumbing services of the building to selected tank

• Every structure installs plumbing services such as PVC pipes to direct rainwater falling on the rooftops to the catch basins of buildings.
• In most cases, the same pipelines can be used to direct the rainwater from the roof to the designed or selected water storage/collection tank.

Step 5: Start Rainwater Harvesting