Rainwater harvesting is done to:
· Ease the demand on the city’s water supply;
· To relieve the seriously depleting groundwater reserves and allow for their levels to rise; and
· Because it’s the purest form of water available requiring practically little or no treatment.
Some of the simplest design include a open basin with some kind of filtration unit. Over the years, rainwater harvesting has steadily gained importance and its designs have gained wide scale publicity. It’s main components include:
1. Catchment: Surface that receives water supply. A variety of plains may serve as catchment areas ranging from rooftops to paved and unpaved open spaces.
2. Coarse Mesh: A large spacing wire mesh is positioned at the entrance of the opening to filter out debris.
3. Guters: Semi-cylindrical conduits that channel water from sloping rooftops to appropriate piping or storage tanks. A 10-15% factor of safety is recommended with reinforcing to support the weight of water.
4. Pipes/Conduits: To transport collected water from one system to another.
5. First Flush Valve: To divert the first flush of water to drains to prevent contamination from settled dust and particulates.
6. Filteration System: A filter unit is required to remove all floatables and suspended particles. Sand filters are easy and economical to use that consist of a layer of coarse media followed by gravel and then sand. Such filters have an added advantage of disinfection as they target microorganisms.
7. Storage Tanks: Various options are available in the market.
International Trends:
Japan: A simple rainwater harvesting system is in place that collects water from rooftops, utilizes a sedimentation tank to settle heavier particles and then transfers the supernatant solution to a sump; from which water is withdrawn with a handpump.
Thailand: Thai harvest rainwater and store it in large jars. They prefer this to other sources of water particularly due to its superior taste.
