JOIN USRainwater harvesting is the conscious collection and storage of rainwater to cater to the needs of water for drinking purposes, domestic use and irrigation. Navita Singh explains how to set up such a sustainable system in your home
Rainwater harvesting is a very important step in the direction of achieving sustainability. It gains significance in a nation like ours where fresh water is a scarce commodity. Rainwater harvesting is the conscious collection and storage of rainwater to cater to the needs of water for drinking purposes, domestic use and irrigation.
Traditional and time-tested systems were employed in the past in various parts of our country. For instance, baoris in Rajasthan, jhalaras in Gujarat, keres in Karnataka and eris in Tamil Nadu. So, the system of harnessing rainwater for future needs is not new to the Indian culture.
It would be advisable to think about rainwater harvesting when you are planning to build your new home. Carefully planned rainwater harvesting scheme will ensure long-term benefits. It is possible to retrofit an existing building but not
without some modifications and additions to the original scheme.
Methods & components
There are mainly two ways of harvesting rainwater — surface runoff and rooftop rainwater harvesting. In urban areas, the natural recharging of the groundwater by rainwater percolation through the soil is reduced drastically as large areas in the cities are paved. The surface runoff rainwater can be harvested to recharge the aquifers. Rooftop rainwater harvesting is the method that is usually employed in homes. The rainwater that falls on the roof is collected and stored in a tank. The main components of the rooftop rainwater
harvesting system are the catchment, transportation, first flush and filter.
Catchment: The catchment area is usually the roof or terrace. The transportation of rainwater should be through the rainwater pipes to the storage tank. Water from sloping roofs should be collected by gutters and directed towards the downpipes.
The roof terrace should be clean and not store chemicals, fertilisers, detergents etc. Gratings or mesh must be provided at the mouth of the drain to trap leaves, debris and other floating materials. The size and the number of downpipes required will depend on the size of the roof. Proper slope should be given to the roof to ensure that the rainwater drains well. The rainwater pipes can be of polyvinyl chloride (PVC) or galvanised iron (GI).
l First flush: First flush is a device used to remove the first rain shower. This ensures that the first spell of rain which carries a lot of pollutants from the roof surface and air does not enter the storage tank. Each rainwater pipe should be installed with the first flush valve device.
l Filters: Filters are used to remove the suspended impurities in the collected water before it enters the storage tank or recharge structure. This unit consists of a chamber with filtering material like sand, gravel, fibre etc. Charcoal can be employed for additional filtration. There are many different types of filters that are used, but the most commonly employed are the sand filter, charcoal filter, PVC pipe filter and sponge filter.
The sand filter contains layers of pebbles, gravel and sand. Each layer is separated by a wire mesh. The charcoal filter is like a sand filter with an extra layer of charcoal. The pipe filter consists of a PVC pipe 1-1.2 metres in length and six inches to eight inches in diameter, depending on the area of the roof. It has compartments that are filled with sand and gravel. The sponge filter is made from a PVC drum having a layer of sponge in the middle. For homes, this is economical to install and easy to maintain.
Many other readymade rainwater filters are also available in the market. A selection can be made on the basis of your requirement, maintenance and cost.
l Storage: The storage tanks can be of different shapes, sizes and materials. The shape can be circular, square or rectangular. They can be constructed from reinforced cement concrete, masonry, plastic or metal. Depending on the availability of space, they could be placed above the ground, partially underground or fully underground. The capacity of the tank has to be carefully designed on the basis of the rainfall received, catchment area and water consumption. Each tank should have excess water overflow system diverting the extra water to a groundwater recharge system. The storage tank may or may not need an electric motor to pump water for usage. This will depend on the location of the tank. Underground tanks usually require a pump for this purpose.
The stored water can be used for washing, cleaning, bathing and gardening. Rainwater is soft, so it is gentle on the skin and hair. It is good for clothes, vessels and appliances like washing machines, dishwashers and geysers. Additional purification through filtration or boiling is required to make it suitable for drinking.
Maintenance
The whole rain water harvesting system should be checked before and after each rain. It should be cleaned at the end of the dry season and before the first rain is expected. The storage tanks should also be scrubbed and disinfected. The filter media should also be cleaned before every monsoon season.
Recharging groundwater
Groundwater should be recharged by using only using rainwater. The easiest thing you could do is to leave maximum plot area for natural percolation of rainwater through the soil. Various types of structures can be created for recharging groundwater, such as percolation pits, recharge pits, recharge trenches and recharging of existing wells and borewells.
We should install rainwater harvesting system in our homes as it has many benefits. It aids in water conservation and leads to a reduction in the expenditure on water bills. It is useful in decreasing surface runoff and soil erosion. It not only prevents the depletion of groundwater but also helps to recharge the aquifers. It resolves the problem of flooding during heavy rains. By adopting rainwater harvesting we will also be ensuring that there are adequate fresh water reserves for our posterity.
Self-reliant model
A R Shivakumar, known as the ‘Rain Man of Bengaluru’, built his home “Sourabha” in 1994, and has not had to pay a water bill in the last 22 years. This rainwater harvesting expert at the Indian Institute of Science says, “We should learn to keep the rain in our homes”.
His 40 X 60 feet plot gets at least two lakh litres of rain every year, which caters to all the water needs of his home.
It rains about 60-70 days in a year and the longest gap between two rains is 90-100 days. A family of four needs between 400 and 500 litres of water everyday.
So, four storage tanks of a total capacity of 45,000 litres were required to be self-sufficient. Each tank has a pop-up filter that has been designed and patented by him.
The waste water from the washing machine and kitchen is also recycled. The water for drinking is filtered by a system that uses silver plate arrangement. Clean and safe potable water is available throughout the year.
(The author is an architect & interior designer)