Rainwater Harvesting-Do it yourself
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Rainwater Harvesting (RWH) is the act of capturing rainwater and either storing it for use or recharging it into the ground. In Apartments, water from clean catchments (roof) can be routed properly through suitable conduits into a filter. Filtered water can be stored in storage structures for subsequent use. Surface run off can be used to recharge the ground water. This is achieved by recharge wells and/or direct tube-well recharge. The following strategy has been found most suitable for rainwater harvesting implementation.
- Storage of rainwater for direct use: Priority is given to capture as much of the run-off rainwater in storage such as sumps, on-ground tanks or tanks on terraces at intermediate levels (e.g.: sit outs / balconies). However for such a strategy, the run-off only from clean areas can be tapped. It is important that these catchment areas be free from any form of chemical or other toxic contamination and dust content is as low as possible. Typically roof areas qualify well for such a strategy. The water from this run-off is first rain separated, filtered and then let into the storage. The water can be used for all household purposes such as bathing, washing, cleaning, gardening etc directly and can even be used for potable purposes if subsequently it is passed through filters to deal with bacteriological contamination (E.g.: aquaguard filters, boiling etc).
- Groundwater recharge: Excess run-off from above mentioned clean surfaces, run-off from other surfaces such as roads, garden area etc can then is redirected for groundwater recharge. The most effective recharge structure has been found to be a recharge well whose depth is a minimum of around 20 feet. These recharge wells recharge the shallow aquifer. Water needs to be distilled adequately before allowing the water into recharge wells. The location of the recharge wells need to be chosen strategically – both where significant run-off water passes through the recharge well location and which is close to existing bore wells. Recharge wells, over time will help replenish groundwater. If the ground water table rises above the bottom of the recharge well, the recharge well can be used as a withdrawal well. The diagram below illustrates the principle of recharge.
Components of Rainwater Harvesting
- Conduit/ Pipes
- Filtration
- Storage Structures
- Recharge Structures
- Conduit/ Pipes: Rainwater pipes/conduits carry water from the roof top to the ground. These pipes have to be connected and drawn to the required location by providing sufficient slope so that the water flows with gravity and no water is stored in the pipes after rain stops. The pipes can also be laid underground but sufficient care has to be taken in order to avoid damage to the pipe because of the vehicular movement. The cost of piping depends on various factors like quality of pipe and length of piping works to be done and many other site conditions.
- Filtration: Rainwater has to be filtered for silt and suspended impurities before allowing into any of the storage structures in order to store it for a longer time. Some of the filtration methods can be implemented.
- First rain separator: It is a mechanism where in first few minutes of rain which carries most of the impurities from the roof are not allowed to pass into the filter or storage structures. It reduces the amount of silt / debris flowing into the filter or storage structures. This in turn reduces maintenance of filter and cleaning of the storage structure.
- Filter: Rainwater from the roof carries dust and suspended particles from the roof top. These impurities have to be filtered before allowing the water for storage. This can be achieved by passing the rain water through a chamber having layers of graded aggregates and a layer of charcoal. The suspended particles get trapped in the aggregate bed and charcoal adsorbs gases and odor if any. Filter also reduces the velocity of water and hence helps in sedimentation of fine particles in the filter.
- Underground / Subsurface Filters: In case it is not possible to provide filters over the ground, underground filters can be constructed. The principle of filtration remains the same but the filter will have 2 chambers with the filter media and the water flows through the filter media and moves to the second chamber through the underground pipe.
- Storage Structures: Rainwater can also be stored in HDPE tanks for secondary uses. This procedure involves construction of a small pedestal and placing the HDPE Tank on the Pedestal and connecting the rainwater pipe to the Tank after First rain Separation unit. The water stored in the rain barrel can only be used for non potable purposes like gardening, car washing etc. Proper overflow pipe should be provided in order to avoid water logging near the rain barrel.
- Recharge Structures: Ground water can be recharged using recharge wells. Ground water recharge helps in reviving the underground water level and can act as an additional source of water if recharged consistently. Recharge wells are constructed by digging the earth, placing concrete rings and packing the outer space of the ring using boulders.
Major Advantages of Rainwater Harvesting
- A well planned RWH system can reduce up to 30% of the water requirement from other conventional sources like bore well or municipal supply.
- Rainwater Harvesting provides reliable supply of water in rainy season.
- Can be a major source of drinking water if the other available sources of water are not fit for drinking.
- Reduces the electrical power consumption as pumping water from deeper bore wells is reduced.
- Reduces the consumption of municipal water hence reduces the stress on centralized water supply board.
- Reduces chocking or flooding of the storm water drains as most of the water is captured at the household level.
- Replenishes the groundwater and secures the availability of water for dry seasons.
