Urban rainwater harvesting system
The components of a typical urban rainwater harvesting system are as follows: -
- Catchments: - It is the surface that directly receives the rainfall and provides water to the system. It can be in the form of a terrace or a lawn or open ground. A roof made up of reinforced cement concrete (RCC), galvanized iron or corrugated sheets can also be used for rainwater harvesting.
- Coarse mesh: - It is present at the roof and it functions as a barrier to the passage of the debris.
- Gutters: - The channels around the edge of a sloping roof are called as gutters. The main functions of gutters are to collect and transport rainwater to the storage tank. Gutters can be in semi – circular or rectangular in shape. It could be made either using galvanized iron sheets or PVC material.
The size of the gutter should be according to flow during the highest intensity rain. It is advisable to make them 10 to 15 % oversize. It is important to support the gutters so as to prevent them from falling off due to water load.
- Conduits: - These are the pipelines or drains used to carry rainwater from the catchment area to the storage tanks. Polyvinyl chloride (PVC) and galvanized iron are the common material used to prepare the conduits.
- First flushing: - A first flush device is a valve that ensures that runoff from the first spell of rain is flushed out and do not enter the system. The first spell of rain carries large amount of pollutants from the air and catchment area and hence first flushing is very essential.
- Filter: - The filter is used to remove suspended matter present in the rainwater. A filter unit is a chamber filled with filtering media such as fibre, coarse sand and gravel layers to remove debris and dirt from water before it enters the storage tank or recharges structure. Charcoal can be added for additional filtration.
When rainwater is harvested in a large rooftop area, the filtering system consists of 3 concentric circular chambers in which the outer chamber is filled with sand, the middle one with coarse aggregate and inner most layer with pebbles.
- Storage facility: - The shape of these tanks can be cylindrical, rectangular or square. Commonly used material of construction includes reinforced cement concrete (RCC), plastic and metal sheets.
Depending upon the availability of space, these tanks could be constructed above ground, partly underground or fully underground.
- Recharge structures: - The ground aquifers may be recharged by the rainwater through suitable structures like dugwells, borewells, recharges trenches and recharge pits. [Top]
Maintenance Tips for Rainwater harvesting structures
- Always keep the surroundings of the tank clean and hygienic.
- Remove Algae from the roof tiles and asbestos sheets before the monsoon.
- Drain the tank completely and clean from inside thoroughly before the monsoon
- Clean the water channels (gutters) often during rainy season and definitely before
the first monsoon rain
- Avoid first 15 or 20 minutes of rainfall depending on the intensity of rain. Use the first
flush arrangement to drain off this first rainwater.
- Change the filter media every rainy season
- Cover all inlet and outlet pipes with closely knit nylon net or fine cloth or cap during
non-rainy season to avoid entry of insects, worms and mosquitoes.
- Withdraw water from the system at the rate of 5 litres/head/day. This will ensure availability
of water throughout the water scarcity period.
- Leakage of cracks in the ferrocement storage tank shall be immediately attended to by cement
plastering. This will avoid major repairs due to the propagation of cracks.
- Heavy loads should not be applied on the lid; particularly many people should not stand on
the lid.
- Water should not be allowed to stagnate in the collection pit.
- The tap should have lock system so that pilferage or waste of water is avoided.
- The filter materials shall be washed thoroughly before replacing in the filter bucket
- The coconut coir in the filter unit definitely needs regular replacement in rainy season,
because, in wet conditions it rots and spoils water quality.
- In coastal areas, the tank may be painted outside by corrosion resistant paint once in 3 years
and in other areas lime (Calcium Carbonate) based white wash may be applied not only for
beauty but also for cleanliness. [Top]
