ROOFTOP WATER HARVESTING
Rain
water harvesting is the accumulating and storing of rainwater for reuse before
it reaches the aquifer. It has been used to provide drinking water, water for
livestock, water for irrigation, as well as other typical uses. The method of
rain water harvesting has been into practice since ancient times. It is as far
the best possible way to conserve water and awaken the society towards the
importance of water. The method is simple and cost effective too. It is
especially beneficial in the areas, which faces the scarcity of water.
During
the monsoons, lots of water goes waste into the gutters. And this is when Rain
water Harvesting proves to be the most effective way
to conserve water. We can collect the
rain water into the tanks and prevent it from flowing into drains and being
wasted. It is practiced on a large scale in metropolitan cities. Rain water
harvesting comprises of storage of water and water recharging through the
technical process. Communities in the face of adversity have revived or created
new water harvesting systems. They have made check dams, johads, and other
structures to harvest every drop of drain. Some of them have even harvested
rooftop runoffs. In many places these efforts have withstood the effects of
recurring drought.
Rainwater harvesting from rooftop
catchments Rooftop Rain Water Harvesting is the technique through which rain
water is captured from the roof catchments and stored in reservoirs. Harvested
rain water can be stored in sub-surface ground water reservoir by adopting
artificial recharge techniques to meet the household needs through storage in
tanks. The main objective of rooftop rain water harvesting is to make water
available for future use. Capturing and storing rain water for use is
particularly important in dry land, hilly, urban and coastal areas.
Rainwater harvesting usually
involves collecting water from cleaner surfaces, such as roofs. There are
several reasons for harvesting rainwater today including: low-cost irrigation,
domestic water supply, water and soil conservation, aquifer recharge, and flood
control. It is also desirable to use rain because of the high quality and
softness of the water and the relative absence of contaminates such as
disinfection by products (chlorinated hydrocarbons), endocrine disrupting
compounds (antibiotics and hormones), heavy metals, agricultural chemicals and
chlorine resistant microbes that are increasingly appearing in our ground and
tap water. Rainwater collection systems are cost effective and easy to maintain
by the average homeowner and are easier to install and use than wells or
surface ponds.
Technical Description
A rainwater harvesting system
consists of three basic elements: a collection area, a conveyance system, and
storage facilities. The collection area in most cases is the roof of
a house or a building. The effective roof area and the material used in
constructing the roof influence the efficiency
of collection and the water quality. A
conveyance system usually consists of gutters or pipes that deliver rainwater falling on the rooftop to cisterns or other storage
vessels. Both drainpipes and roof surfaces
should be constructed of chemically inert materials such as wood, plastic, aluminum, or fiberglass, in order to avoid adverse
effects on water quality.
The water ultimately is stored in a storage tank or cistern, which
should also be constructed of an inert material, Reinforced concrete, fiberglass,
or stainless steel are suitable materials. Storage tanks may be constructed as
part of the building, or may be built as a separate unit located some distance
away from the building.
A
rainwater harvesting system comprises components of various stages -
transporting rainwater through pipes or drains, filtration, and storage in
tanks for reuse or recharge. The common components of a rainwater harvesting
system involved in these stages are illustrated here.
1. Catchments: The catchment of a water harvesting system is the surface which directly receives the rainfall and provides water to the system. It can be a paved area like a terrace or courtyard of a building, or an unpaved area like a lawn or open ground. A roof made of reinforced cement concrete (RCC), galvanised iron or corrugated sheets can also be used for water harvesting.
2. Coarse mesh at the roof to prevent the passage of debris
3. Gutters: Channels all around the edge of a sloping roof to collect and transport rainwater to the storage tank. Gutters can be semi-circular or rectangular and could be made using:
Locally available material such as plain galvanised iron sheet (20 to 22 gauge), folded to required shapes.
Semi-circular gutters of PVC material can be readily prepared by cutting those pipes into two equal semi-circular channels.
Bamboo or betel trunks cut vertically in half.
The size of the gutter should be according to the flow during the highest intensity rain. It is advisable to make them 10 to 15 per cent oversize. Gutters need to be supported so they do not sag or fall off when loaded with water. The way in which gutters are fixed depends on the construction of the house; it is possible to fix iron or timber brackets into the walls, but for houses having wider eaves, some method of attachment to the rafters is necessary.
4. Conduits: Conduits are pipelines or drains that carry rainwater from the catchment or rooftop area to the harvesting system. Conduits can be of any material like polyvinyl chloride (PVC) or galvanized iron (GI), materials that are commonly available.
5. First-flushing: A first flush device is 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.
6. Filter: The filter is used to remove suspended pollutants from rainwater collected over 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 recharges structure. Charcoal can be added for additional filtration.
I. 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.
II. Sand filters: 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. In a simple sand filter that can be constructed domestically, the top layer comprises coarse sand followed by a 5-10 mm layer of gravel followed by another 5-25 cm layer of gravel and boulders.
7. Storage facility: There are various options available for the construction of these tanks with respect to the shape, size and the material of construction.
Shape: Cylindrical, rectangular and square. Material of construction: Reinforced cement concrete, (RCC), ferro cement, masonry, plastic (polyethylene) or metal (galvanised iron) sheets are commonly used. Position of 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.
8. Maintenance: -
o Before collecting water the roof, gutters and tank should be cleaned
o Let the first 2-3 rains flow out through the first flush system
o Remember to clean the tank once in a year
o Replace the filtering agents every year
o Keep the tank and surroundings clean and hygienic
o Apply white cement on the tank every year
o Make sure that sunlight does not pass through the manhole to prevent algae growth
o Remember to preserve water and use it judiciously
