Rainwater Harvesting and its Benefits

By N Munal Meitei *

A Rainwater Harvesting technique

Myself, in my childhood, when the elders asked me not to use more water, I thought, water has unlimited resource and we shall be getting our requirement endlessly. At that time in each of the homesteads, there were ponds and people were unaware of water scarcity but now owing to overpopulation and congestion, the ponds have vanished.

The important of water seems to be clear year by year. People say, there are the five vitals of the life such as Fire, Water, Air, Earth and the Sky. Amongst these, the unavoidability of water has come up. Water is life. Man can live without food for more than one month but without water man cannot live more than seven days.

Water is so precious that if and another third World War is to be occurred, then that will be the war of Water. We know that about 70% of the earth's surface is covered with water. But only 3% of the water found on earth is palatable and rest is in the form of sea water and ice. Out of this palatable water, the maximum portion is also in the lakes, rivers and as ground water.

A meagre portion is available with us for our utility. As per the reports from the United Nations, one person in every three in the world are facing water crisis. The year 2003 was celebrated with the World Environment Day theme as "Water - Two Billion people are dying for it!" and 2004 as "Wanted! Seas and Ocean- Dead or Alive?".

Therefore to meet this water problem, there have been the practices of techniques like Dew Pond and Air Well etc to catch and store whatever the possible water from all sources. Seeing such water scenario, we need to use water judiciously and need to search the alternative means. Rain water harvesting is a very easy and reasonable means of water supply in our present day life particularly in our hilly State like Manipur.

There is great variation in the amount of water consumed per day all over the world. At home in the United States, each person uses about 250 litres of water per day. Typical cruising yachts use about 6 litres per person per day, the average probably. The minimum water intake required to maintain body hydration is 1.5 litres per day.

The maintenance of comfort under normal circumstances requires 3% of mass body weight or typically about 2.3 litres per person of drinking water per day. But in Manipur, we find that for a family residing in the hill villages could collect only about 10-15 litres from a far flung place for the whole family use of 6-8 members. Please feel the differences. Therefore, rain water harvesting is the best option.

The principal of collecting, storing and using precipitation of rain water from a catchment surface before it reaches the aquifer is called rain water harvesting. Rain water harvesting systems are simple to install and operate. Rain water can supplement the sub soil water level and increase urban greenery. Water collected from the ground, sometimes from areas which are especially prepared for this purpose, is called storm water harvesting.

In some cases, rainwater may be the only available or economical water source. Rain water harvesting systems can be simple to construct from inexpensive local materials, and are potentially successful in most habitable locations. Roof rainwater can't be of good quality and may require treatment before consumption. As rainwater rushes from roof, it may carry pollutants in it such as the tiniest bit of mercury from coal burning and bird feces.

Although some rooftop materials may produce rainwater that is harmful to human health, it can be useful in flushing toilets, washing clothes, watering the garden and washing cars; these uses alone halve the amount of water used by a typical home. Household rainfall catchment systems are appropriate in areas with an average rainfall greater than 200 mm or 7.9 inches per year, and no other accessible water sources (Skinner and Cotton, 1992).

Overflow from rainwater harvesting tank systems can be used to refill aquifers in a process called ground water recharge. Ground water is one of the inevitable sources of water in the maximum of the modern urban areas. There are a number of types of systems to harvest rainwater ranging from very simple to the complex industrial systems.

The rate at which water can be collected from either of the system is dependent on the plan area, its efficiency, and the intensity of rainfall i.e. annual precipitation (mm per annum) x square meter of catchment area = litres per annum yield e.g. a 100 square meter roof catchment catching with 1,000 mm rainfall will have annual yields of 100 kLPA (taking 100% efficiency).

Components of Rain Water Harvesting

Rain water collection may be from roof tops, terrace, courtyard, paved or unpaved open ground etc. But Roof water harvesting system which is the simplest and easiest will be the most suitable method for Manipur. It has the components like Catchment area, Collecting Gutters, Transportation, First flush, Filter and Storage tank.

Down pipe and first flush arrangement

This is an arrangement to prevent the dust and other unwanted materials that may be seen on the roof, from reaching the storage tank. By fitting a down pipe with an end cap or valve can ensure that the washed water from the roof does not reach the storage tank. It is always safe to ensure that the first flush arrangement remains open during non- rainy days and should be closed after first rain up to the satisfaction of the end user.

Filter unit

The rainwater collected from the roof should be allowed to reach the storage tank only through a filtering mechanism. Rubble, sand and charcoal, as used in the traditional three-pot filtration, can be adopted here. 10 cm thick 20mm rubbles, 10 cm thick charcoal/coconut shell, 15 cm thick coarse sand, 5 cm thick 6mm rubbles etc. may be arranged from bottom to top in the filter unit. The water that is passed through this filter should remain safe for a long period of storage. Charcoal/coconut shell is added to eliminate gaseous pollutants.

Storage tank

Mainly three types of storage tanks are constructed for roof water harvesting. They are above ground, underground or sub surface tanks as per requirement. The storage tank may simply be the collection drums.

Provision for drawing water and spill over

For drawing water from the storage tanks, any method may be adopted provided it shall be drawn only when needed. The easier the method adopted for drawing water, the more will be the chances for its misuse. The adopted methods may be a tap, hand pump or electric pump sets.

Maintenance

• Before collecting the rain water, the roof, gutters and tank should be cleaned
• Let the first 2-3 rains flow out through the first flush system
• Remember to clean the tank once in a year
• Replace the filtering agents every year
• Keep the tank and surroundings clean and hygienic
• Apply white cement on the tank every year
• Remember to preserve water and use it judiciously

Advantages of Rain Water Harvesting

Rainwater harvesting systems are simple to install, operate, and maintain. It is convenient in the sense that it provides water at the point of consumption and operating costs are negligible. Water collected from the roof catchment is available for use in potable and non-potable applications such as toilet and/or urinal flushing, laundries, mechanical systems, custodial uses, site irrigation and for bathing water. Since rainwater is collected using existing structures, i.e., the roof, rainwater harvesting has few negative environmental impacts.

Benefits of Using Rain Water Harvesting

Rainwater is free; the only cost is for collection and use. It lessens demand on the municipal water supply. It saves money on utility bills. It makes efficient use of a valuable resource. It diminishes flooding, erosion, and the flow to storm water drains. It reduces the contamination of surface water with sediments, fertilizers and pesticides from rainwater run-off resulting in cleaner lakes, rivers, oceans and other receivers of storm water.

It can be used to recharge ground water. It is good for irrigation and plants thrive because stored rain water is free from pollutants as well as salts, minerals, and other natural and man-made contaminants. It is good for laundry use as rain water is soft and lowers the need for detergents. It adds life to equipment dependent on water to operate, as rain water does not produce corrosion or scale like hard water. It can help achieve LEED Green Building Rating Credit.

What are the benefits of rain water collection?

Rain water is the purest form of water. In rain water, we have total control over our water supply. It is very ideal for cities with water restrictions. It is socially acceptable and environmentally responsible. It promotes self-sufficiency and helps conserve water. Rain water is better for landscape plants and gardens because it is not chlorinated. It reduces storm water runoff from homes and businesses. It can solve the drainage problems on your property while providing you with free water.

It uses simple technologies that are inexpensive and easy to maintain. The potential cost savings especially with rising water costs. It can be used as a main source of water or as a backup source to wells and municipal water. The system can be easily retrofitted to an existing structure or built during new home construction. Systems are very flexible and can be modular in nature, allowing expansion, reconfiguration, or relocation, if necessary. It can provide an excellent back-up source of water for emergencies.

Rain Water Harvesting in Manipur

There are good opportunities for rain water harvesting in Manipur because Manipur is blessed with monsoon type of climate. We face severe water scarcity during the dry spells of winter every year. During rainy season also, there are problems for shortages of drinking water. In spite of having numerous rivers and many wetlands and groundwater availability, the State is facing water scarcity even though it receives 1790 mm of average rainfall, which is around 3 times the Indian national average.

The high variations in spatial and temporal rainfall add to the complexity of problems associated with water management faced by the State. The ground water available in the Thoubal district mainly in Kakching area has been proved to be excessively contaminated with health hazard arsenic. Therefore Rain water harvesting is a vital alternative source.

The State experiences the specific climate with appreciable variation showing highly contrasting meteorological conditions. The annual precipitation varies from 2194 mm to 4516 mm as recorded in the western region and 2943 mm in the south and 1785 mm in the central part of the State. The rainfall is unevenly distributed throughout the year.

Out of the existing houses of the State, about 50% of the houses mostly in the rural areas consists of galvanized corrugated iron slanted roof sheets and about 20% houses mostly in the towns are RCC buildings and the remaining are thatched roofed houses in the village areas. Most of the Community halls, Churches, Schools, Temples etc. in our State have CGI roofs. Though these CGI sheets roofs are much suited for rain water collection system, we are yet to implement it.

In the hill areas the maximum of the houses are with thatch roofing and hence the utility for Rain water harvesting is limited. But after some simple treatments, this water can be well utilized for all proposes. The soils of the hill areas are also porous and cannot hold water for a longer time.

For a poor family to construct high quality storage tank may not be possible, therefore the best method will be construction of katcha ponds lining with tarpaulin. Collection of Rain water in the drums is also another feasible way. If the Harvesting is to be done for the whole village, then a bigger ferro-cement tank with roof may be constructed.

Therefore, we should not leave the advantages of Rain water harvesting. A GCI roofing house having a surface area of 30 ft. X 40 ft. can collect about 1,49,500 litres of water per annum while the average rainfall is calculated at 1790 mm and efficiency for 75%. If the Govt. has the plan that every new house constructed in the state are compulsorily to have the water harvesting facility, then 50% of our water problem will be solved.

While each of the houses have the Rain water harvesting facility, then the problem for over flow on the Roads and Nalas in most of the localities with a little shower will be solved. If done so, each of the family will have self treated and clean water independently.

Rain water harvesting will particularly benefited the hill dwellers as the water problem is more acute for them. The Municipal councils, Small town committees and Panchayats also should have their own Rain water harvesting facilities to help the public supply, to improve the ground water condition and for more greenery.

The national flagship programme such as MGNREGS should also aim for most of its projects to Rain Water harvesting facilities for free water and developed rural area. Therefore, it is our own duty, the duty of the citizen of India to harvest water, save it and utilized it judiciously.

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* N Munal Meitei wrote this article for The Sangai Express
The writer is a Range Forest Officer and he can be reached at nmunall(at)yahoo(dot)in
This article was webcasted on September 20, 2011.

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