What is Rainwater Harvesting?

Rainwater Harvesting, also referred to as RWH, is a simple method of collecting rainwater and deploying the same for further usage. This is an increasingly important water conservation method in apartments and gated complexes. It is popular because it can result in significant savings and is easy to implement.

Expert Water Conservation Tips

This is the best and most effective method of harvesting rainwater for apartments as it is less expensive and if implemented efficiently, helps in augmenting the groundwater level of the area. This is a system of catching rainwater where it falls. In this method, the roof becomes the catchment, and rainwater is collected from the roof of the building, which can either be stored in a tank or diverted to an artificial recharge system.

Components of Rooftop Rainwater Harvesting

The process involves transporting rainwater through pipes and drains, filtration and storage for reuse/recharge. Here are some common components involved in these stages:

1. Catchments: Surface which directly receives the rainfall and provides water to the system. It can be a paved area such as a building terrace or courtyard, or an unpaved area such as a lawn or an open ground. A roof made of reinforced cement concrete (RCC), galvanised iron or corrugated sheets can also be used.

Vikas Complex Cooperating Housing Society in Thane (W), successfully collected 59,1260 litres of water from a Catchment area of about 296 square metres (sq. m). Whereas, the average annual rainfall in Thane is about 2350 millimetre (mm).

2. Channels: Water is collected around the edge of a sloping roof in channels and is carried to a storage tank. The size of the channel depends on the flow during heavy rain. It is advisable to make them 10 to 15% larger. They can either be made from plain galvanised iron (GI) sheet, polyvinyl chloride (PVC) or even bamboo trunks.

3. Conduits: Pipelines or drains that transport rainwater from the catchment area to the harvesting system. Conduits can be of PVC or galvanised iron.

4. First-Flushing: A valve that ensures that runoff from the first spell of rain is flushed out and does not enter the system. This needs to be done since the first spell of rain carries a relatively larger amount of pollutants from the air and catchment surface.

5. Filter: Removes suspended pollutants from rainwater collected over the roof. 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 recharge structure.

Types of Filters:

  • Charcoal water filter: A simple charcoal filter can be made in a drum or an earthen pot. The filter is made of gravel, sand and charcoal, all of which are easily available.
  • Sand filter: Sand filters have commonly available sand as filter media. Sand filters are easy and inexpensive to construct. These filters can be employed for treatment of water to effectively remove turbidity (suspended particles like silt and clay), colour and microorganisms.
  • Rainwater Purification Centre (RainPC): A system designed for the conversion of rainwater to drinking water. Coming in a small compact 26 kg unit, the RainPC offers an affordable solution.

6. Storage Facility: There are multiple options available based on the shape, size and material of construction.

  • Shape: Cylindrical, Rectangular and Square
  • Material: Reinforced cement concrete (RCC), ferrocement, masonry, plastic (polyethylene) or metal (galvanised iron) sheets
  • Position of the tank: Depending on space availability, these tanks could be constructed above ground, partly underground or fully underground. Some maintenance measures like cleaning and disinfection are required to ensure the quality of water stored in the container.

7. Recharge Structures: Rainwater may be charged into the groundwater aquifers, an underground layer of water-bearing permeable rock, rock fractures or unconsolidated materials such as gravel, sand, or silt, through any suitable structures like dugwells, borewells, recharge trenches and recharge pits.

  • Recharge trenches and permeable pavements: These recharge structures promote the percolation of water through soil strata at shallower depth.
  • Recharge wells: These structures conduct water to greater depths from where it joins the groundwater.
  • Recharge pits: The excavated pit, 1.5m to 3m wide and 2m to 3m deep, is lined with a brick/stone wall with openings (weep-holes) at regular intervals. The top area of the pit can be covered with a perforated cover. Design procedure is the same as that of a settlement tank.

For further details visit www.enviroconnect.co.in

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