RAIN WATER HARVESTING

Article submitted by

Adelabu Gerard Oluwaseun  [professional Member]

[Accepted 17th Jan. 2016]

According to the United States Geological Survey, (USGS) about 71% of the Earth's surface is covered by water. This means that the oceans hold most of Earth's water. However, There is also freshwater stored in the ground which is man's preferred source of fresh water.

Rainwater emanates originally from surface water which is found in oceans, seas, lakes, ponds etc.  Through continuous evaporation from the surface of the Earth, water vapor collects in the clouds. When all the vapor condenses and reaches a point of sublimation, it pours down in form of rainfall. Some part of this rain water infiltrates into the ground and is stored there as ground water while the rest runs off on the ground surface and back into the rivers and water bodies from where they evaporate again into the clouds. Plants absorb a portion of the surface runoff and groundwater which aids its food production. Eventually they also lose some portion by evapo-transpiration through their leaves.   All the evaporated water from the surface of oceans, plants and surface run-offs, are collected in the cloud and stored there for a period of time. When the clouds become saturated with water vapor, to a point where it can hold  no more, the vapour condenses and is released again in form of rainfall and the cycle continues.

A close study of the water cycle points to the fact that; all other things being equal, the oceans are presently holding enough water in the world to serve us another millennium. The challenge however is that; this ‘water’ is out there in the oceans. we typically draw ground water for our immediate building use and not ocean water. This groundwater, being the golden source of fresh water is being depleted faster than it can recharge. Other inhibiting factors are first, the ‘cost’ element associated with digging to reach groundwater and the energy required to send this water to individual apartments continuously to cater for an ever widening array of needs. This is worse in areas where ground water table is low or fluctuates with the seasons e.g. in sub-Saharan Africa.

Second is the challenge experienced in desert areas, where annual precipitation is too low to sustain any vegetation. Such areas witness sparse rainfall most of the year and sometimes no rain at all with maximum temperatures of 39⁰C (102⁰F) and above during summer e.g: countries in the northern part of Africa and parts of western and central Australia. Such areas are forced to rely on artificially supplied water, sometimes employing the use of aqua ducts and covered earth pipes of various types that are built to convey water from nearby oceans or seas.

Whichever the case, Ethical environmentalists preach the need for water conservation practices to all building users of different climatic backgrounds. This has to do with employing methods and practices that save as much water as possible by adopting alternative methods and re-use or recycle of waste water from homes and offices. Thereby reducing the energy required to provide more water as well as the cost. It is a principal requirement for water efficiency.

THERE ARE SEVERAL APPROACHES TO WATER CONSERVATION IN GREEN BUILDINGS, THEY INCLUDE: 

• Use of low flow shower heads, taps and toilet flushers : These are specially built to dispense water at varying pressures for different purposes. This helps ensure that water is not wasted when performing tasks that require only a little amount of water. This is used in toilets and baths of green homes.
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• Automatic shut-off sinks : This are programmed to automatically start and stop dispensing water according to detected motion. This helps ensure that water is not lost due to carelessness or forgetfulness of the users. It is helpful in public buildings.
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• Water - less urinals : This entails replacement of water-urinals with chemical disinfectant -urinals. The chemicals help control the urine odor with little or no water required.
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• Steam trap programs : This is used in buildings with well developed heating systems such as factories, where heat is a principal element for production. The steam residues after the product is heated can be collected and stored for reuse. This method is common in developed countries.
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• Storm water collection : During Rainfall, the water that runs off on the ground surface, can be collected and channeled to Earth - Recharge tanks, instead of allowing them to run off into gutters and away from the site. To do this, the surface finish of the site must be permeable enough and well sloped to the drain point.
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•  Re-use of by-product water : Industries that use water in production and processing, can reclaim as much water as possible, for other needs such as landscaping and flushing.
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• Rain water harvesting : Africa and other communities have collected and re-used rain water for centuries. Traditionally it entails collecting water run-off from roof of buildings through gutters and downspouts directed to storage tanks or cisterns from where they are either purifed or simply re-pumped to an overhead tank for use in the building. This helps immensely to reduce the consumption of fresh water from the ground or cost and demand of external water supply to the building.

ADVANTAGES OF RAIN WATER HARVESTING

1. This approach is simple and requires low maintenance.
2. It is a money saving source of high quality water.
3. It helps reduce the burden on drainage systems due to high volume of surface run-off water.
4. It is an invaluable source of fresh water for remote areas or desert areas with little precipation.

FACTORS TO BE CONSIDERED WHEN CONSIDERING RAIN WATER HARVESTING INCLDUE:

1. Expected volume of rainfall, this is to determine whether it is worth the trouble.
2. How much water is needed to cater for the building needs.
3. Total area of the roof that is available for collecting rain.
4. How much water will not go into the tank, the loss factor.
5. The Tank size to be provided.
6. Position of the drain pipes and collection tank or tanks to maximize output.

References:

http://www.askbuild.com/cgi-bin/column?097
http://www.southwall.com/products/heatmirror.html
http:/www.gri.org
http://www.greenbuilder.com/sourcebook/energy_recovery_vent.html

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