Rainwater Harvesting: How it works? What to do?

Catch water where & when it falls - Every raindrop matters now, when the whole world is staring helplessly at a never-before-kind-of water scarcity.
Collecting and storing of rainwater for reuse, rather than allowing it to run off, is possibly the only way out of persistent droughts. Why?

Whatever your Government can do, it CANNOT create water.

The idea behind the process is simple and ancient. Rainwater is collected when it falls on the earth, stored and made use at a later point. A few basic elements are commonly required to all RWH - RainWater Harvesting systems.

• 1. Catchment area
• 2. Conveyance system
• 3. Filter system
• 4. Storage area
• 5. Recharge area

1. Catchment Area

This is where the rain falls. Clean catchments are necessary for maximising the harvest. Based on this criteria, the harvesting method differs.

Rooftop Harvesting

Roofs today have become the place for solar panels, wind generators, gardens. So harvesting rooftop water is a comparitively simpler process; All you need is a clean terrace, a pipe to connect the roof and storage, and a filter to screen the dust particles.

Construct an underground storage tank. If you plan to recharge the aquifers, setup an unlined pit containing layers of gravel and sand to filter out mud.
Note: This pit should be about atleast 1.5m deep, so that it never overflows. This allows water to percolate into the ground.

Setback Harvesting

Setback area typically includes the driveway, balcony, garden and front yard. Rainwater harvesting structures should not be constructed at any place, without paying heed to the nature of the soil.

• In Rocky terrain, water can be stored in sumps as groundwater recharge is not possible.
• In Clayey region, if it doesn’t turn sandy beyond 15 feet, a small hole can be dug up within a recharge well and a pipeline of 6 inches can be inserted to take the water to a deeper level.
• in Sandy coastal areas, A well of 3 feet to 5 feet diameter would suffice in sandy regions. Leaving the open areas unpaved would itself result in percolation of surface runoff, thus recharging the groundwater.

 2. Conduit System 

Conveyance of rainwater is through the channels built around the edge of a slanting rooftops to direct water flow from the catchment area to the storage area. These gutters can be made using galvanized iron sheets, PVC material, bamboo or betel trunks.

 3. Filter Systems

Four types of filtration processes can be employed in an RWH system:

Screening: 

This first level process involves filtering out gross pollutants like leaves, droppings and other materials.

First flush: 

At the second level, a valve is fixed to ensure the bifurcation of the first few minutes of the rainwater, which collects dust & other contaminants.

Filtration: 

Next level filters remove dissolved organic and inorganic particles in the rainwater, before it is collected. Such filter screens all dust particles .

Settlement tanks: 

Settling tanks remove silt and other coarse materials.

Note:

2 options are available to make use of the harvested rainwater:

• * Storing in receptacles

• * Recharging into aquifer

 4. Storage Area

Rainwater from the roof is stored in sumps (underground water storage tanks). Households that have structures, connected to sumps report that good recharge takes place with only 1/3rd length of filters filled up. However, problems relating to cleaning of sumps and their limited durability are the chief concern.

5. Recharge Area

Surface run-off water is mainly used to recharge the soil. Such recharge happens by either percolation pits or recharge well methods.

Note: 

• Identify the recharging zones

• Ensure the quality of rainwater

• Avoid groundwater pollution

Perforated slabs and paving alternate sections allow for increased percolation. However, usage of pebbles can get the percolation pits silted easily. Cleaning of which may not be easy, as it almost resembles a deep borewell.

A recharge well without a filter medium is the best option in most cases, as soil can facilitate natural filtration.

Advantages of harvesting Rainwater

Personal Gain

• The rainwater that falls on your roof and property is essentially free. 
• Water can be used for several non-drinking purposes in both residential and commercial properties.
• Collecting & using rainwater to replace municipal water, reduces your water bill.
• Rainwater can be used for irrigation, or as non-potable water used indoor, or even as potable water supply.

Global Gain

• Ever-increasing demand for ground water can be reduced, especially in areas where water-table had gone down.
• The large capacity storage tanks that collect rainwater can reduce floods in some low lying areas.
• Reduced runoff can bring down the contamination of surface water with pesticides, sediment, metals, and fertilizers.
• Rainwater, free from several pollutants, man-made contaminants and chlorination is ideally suited for plants and landscape irrigation.