Rooftop rainwater harvesting for domestic water supply in Manipur

Dr. Laishram Kanta Singh, Dr. S. Roma Devi, Dr. Arati Ningombam, Mrs K Lily Rangnamei *

The process by which rainwater is collected from roof catchments and stored in reservoirs is known as rooftop rainwater harvesting. By using artificial recharge techniques, collected rainwater may be stored in subsurface ground water reservoirs to provide the demands of the family through tank storage. Making water accessible for future use is the primary goal of rooftop rainwater harvesting.

Rooftop harvesting is collecting rainwater from a building's or home's roof by turning it into a catchment. It can be either directed to an artificial recharge system or kept in a tank. If used correctly, this technology, which is less expensive and extremely successful, contributes to raising the local groundwater level.

Every one of the following components of the RWH structure may be found on the roof of any building, no matter how big or little. The catchment area, conveyance, flushing, and filter medium (Sand gravel filter/Charcoal filter) make up the majority of the RWH system. Rain water from the roof is collected, stored, and used directly or used to replete the groundwater table.

Need for Rooftop Rain Water Harvesting

1. To meet the ever increasing demand for water
2. To reduce the runoff which chokes storm drains
3. To avoid flooding of roads
4. To augment the ground water storage and control decline of water levels
5. To reduce ground water pollution
6. To improve the quality of ground water
7. To reduce the soil erosion
8. To supplement domestic water requirement during summer, drought etc.

Advantages of Rain Water Harvesting

1. Provides water supply with self-sufficiency
2. Provides high-quality water that is soft and low in minerals
3. Lowers the expense of pumping ground water
4. When recharged to ground water, it dilutes the water, enhancing its quality.
5. Minimizes urban soil erosion
6. Rooftop rainwater collection costs less money
7. In hilly terrains, rainwater harvesting is preferred.
8. Rooftop rain water harvesting systems are simple to build, operate, and maintain.
9. Rainwater harvesting is preferred in saline or coastal areas.
10. In saline or coastal areas, rainwater provides good quality water. When recharged to groundwater, it reduces salinity and also helps to maintain balance at the fresh-saline water interface.

Safety Consideration in Storage of Groundwater Reservoir

1. To prevent the wells from being soiled, a filter or desilting pit should be supplied for rooftop rainwater gathering using existing tubewells and handpumps.
2. If such tubewells are pumped sporadically, recharging efficiency is increased.
3 . An inverted filter may be offered if the groundwater reservoir is refilled by a shaft, drilled well, etc.

Safety Consideration in Storage Tanks

1. A storage tank shouldn't be placed near a source of pollution, such a septic tank or another similar structure.
2. In order for a storage tank to fully fill, it must be situated below the roof.
3. The installation of an overflow pipe that discharges into a non-flooding region is required for a rainwater system. Additional water may be utilised to recharge the aquifer by a tubewell, abandoned handpump, or other means.
4. To prevent disturbing the filtering material, a speed breaker plate must be installed below the intake pipe in the filter.
5. Cleaning of storage tanks should be possible.
6. The entry into the storage tank should include screens that can be easily cleaned.
7. Before utilising water for drinking, it can be routinely disinfected using methods such as boiling or chlorination.

Estimation of rooftop rainwater harvesting

The effectiveness of collecting rain relies on a number of factors. Depending on the exact design, collection efficiencies of 70-80% are frequently employed. Finding out how much water would be produced by your roof area is the first step. For this, the typical monsoon rainfall is employed.

Total quantity of water to be collected (cu. m) = Roof Top Area (sq. m) x Average Monsoon Rainfall (m) x 0.8

Design of rainwater harvesting storage

Calculating demand of building users (for RWH storage):
X = 135 litres of water used per capita per day (standard for calculation)
Y = Number of residents/users
Z = 30 days in a month (average)

Monthly water demand of unit = X * Y * Z The materials used to construct the roof must be non-toxic and chemically inert. Smooth, firm, and thick roof surfaces are best because they are simpler to clean, less likely to be damaged, and less prone to discharge materials or fibres into the water. Since the majority of paints contain harmful materials and may peel off, painting a roof is not advised.

There should be no overhanging trees left close to the roof. Bird nesting on the roof ought to be avoided. To keep out leaves and other debris, all gutter ends should be equipped with a wire mesh screen. Make the proper arrangements to dispose of the initial flow of rainwater. At water outputs, a sanitary soak away channel and a screened over flow pipe have to be constructed.

The storage tank should have a manhole cover, a flushing pipe at the bottom, and a tightly fitting roof that blocks light (for standing tanks). To prevent contaminating the water in the tank, a dependable sanitary extraction method like a gravity tap or a hand pump should be present.

No chance of tainted wastewater entering the tank should exist (especially for tanks installed at ground level). It is not recom mended to empty water from other sources into the tank through pipe connections or the manhole cover unless the source is trustworthy.