Rainwater harvesting: A sustainable solution to water shortage

 
The ancient Chinese theory of the “Five Elements” holds that the world is formed of five materials:  water, earth, wood, metal and fire. For water to be listed as one of the five basic elements indicates its importance. Here, water primarily refers to rainwater, the use of which can be traced back to the primitive society.

In Ghana, persistent water shortage situations are part of normal everyday life in many rural settlements and some urban centres, particularly the peri-urban areas.

Many communities in several parts of the country still rely on surface water such as streams, rivers, lakes, ponds, dug-outs and reservoirs. These sources often serve as drinking places for animals as well.  The health hazards posed by this situation are far reaching.

History of rainwater harvesting
Tracing the history of rainwater harvesting, Ing Dr Frederick Amu-Mensah of the Water Research Institute of the Council for Scientific and Industrial Research said rainwater harvesting was the oldest technology developed by man to provide water for domestic use, adding that in Ghana the challenges posed by dry wells as well as excessive levels of contaminants, especially high concentrations of some undesirable minerals in the ground water resources of some geological formation, made harnessing of rainwater for household use very necessary. 

He enumerated the methods of rainwater harvesting in the past as collection via roof gutters from rooftops of buildings with corrugated iron sheets and other materials such as thatch, bamboos, coconut/palm branches, cocoa leaves and the back of trees, among others.

He said other techniques for harvesting included scooping rainwater from depressions and potholes on roads or road sides, harvesting the rainwater directly from the atmosphere and the collection of rainwater or dew from leaves or roof system.

He stated that currently, in the urban communities, very little is done to harvest rainwater despite the poor water network  in place. He observed that even though urban dwellers had better roofs, they still did not harvest rainwater to supplement what they got from the Ghana Water Company Limited, indicating that rainwater harvesting was still very popular in rural communities despite their poor roofing system.

Benefits of rainwater harvesting
The benefits of rainwater harvesting include relief from other expensive water supply systems, ability to farm or build in areas with no other water supply, increased independence and own water security, lower water supply cost, reduced flood flows, especially in urban areas prone to flood, reduced topsoil loss due to erosion, improved plant growth, it is gentler on equipment and piping because no scaling occurs. It also prevents breeding of mosquitoes and sources of water-borne diseases.

Treatment and use
The raindrop, as it falls from the cloud, is soft, and among the cleanest of water sources.

Irrigation with captured rainwater promotes healthy plant growth. It also extends the lifespan of appliances as it does not form scale or mineral deposits in them.

Though the environment, the catchment surface, and the storage tanks affect the quality of harvested rainwater, with minimal treatment and adequate care of the system, rainwater can be used as potable water as well as for irrigation.

Contaminants captured by the rain from the catchment surface and storage tanks are of great concern to users of rainwater for potable use because the catchment areas may have dust, dirt, faecal matter from birds and small animals and plant debris such as leaves and twigs.

Therefore, rainwater intended for domestic potable use must be treated using the appropriate filtration and disinfection methods. 

The various types of treatment employed in rainwater harvesting system include settling sedimentation and activated charcoal, disinfection such as boiling or distilling, using filtration, roof washers and straining or sand filtration. Other more efficient but expensive systems include catrigde filters, ultra-violet (UV) irradiation and reverse osmosis (RO) systems.

Rainwater for better sanitation, health and agriculture

Touching on the quality of harvested rainwater, Ing Dr Benjamin Sabi of the Department of Agriculture Engineering of the University of Ghana said rainwater which had been properly collected and stored was expected to be substantially free from minerals and most of the common pollutants that were present in surface and ground water sources.

He said rainwater lacked minerals and other chemical substances of river water and ground water, adding that it was designated as soft water and lathered easily. “It also does not form scale in pipes and is therefore friendly to equipment. It has the highest capacity of all water to dissolve substances because of its purity”. He said.

According to him, roofing materials made from metals that did not corrode easily were unlikely to impact on the quality of the harvested rain. He observed that local materials such as thatch may impact on colour, turbidity and taste of the water, adding that in the rural environment where industrial activities were low, production of gases such as carbon monoxide, hydrogen sulphide and hydrocarbons may not affect the quality of rainwater.

Dr Sabi said rain was the source of water for rivers, lakes and ponds and all fresh water on lands, adding that it had been used exclusively to serve the needs of entire cultures as in the case of ancient civilisation of southern Israel or for supplementary purposes as in the case of the ancient civilisation of Egypt and Rome whose entire irrigated agricultural production had been practised from rainwater harvesting.

Observations
Currently, the increasing populations of urban areas, resulting in the spread of the boundaries of cities are presenting a new dimension to the need to harvest rainwater. Natural lands with vegetative cover ensures a balance of runoff flows during rainfall. When these lands are cleared for development, this balance is compromised and excessive erosion and run-off flow result. 

Since water flows from higher points to lower points, the low lying areas of Sakaman etc. will increasingly be subject to flooding because rainwater from as far as Madina and Ashongman eventually end up at these low lying locations. It is, therefore, very crucial that rainwater harvesting should be looked at not only as a means of providing more water for domestic uses in every home but also as a means of reducing flooding. If not taken seriously, the comtinous expansion of urban areas will negatively affect its low lying areas.

To this end, the enforcement of the building code in regard to the provision of rainwater harvesting in especially new buildings as a pre-requisite to obtaining a building permit must be religiously upheld.

CSIR interventions
With funding from the Nordic Climate Fund, CSIR Water Research Institute in collaboration with SINTEF of Norway the CSIR Science and Technology Policy Research Institute are piloting 20 domestic rainwater harvesting systems in Accra to promote the technology, standardise the systems for easy replication, train artisans in the installation process, encourage business in rainwater harvesting and provide an adaptation strategy for dealing with climate change impacts.

Some important aspects of rainwater harvesting
There are various aspects to rainwater harvesting aside from water provision, irrigation and flood control. Excess rainwater can be used to recharge aquifers. Industrial water needs can be satisfied by rainwater harvesting. Aquaculture and ecosystem protection can be enhanced and sustained with rainwater harvesting. Firefighting is another important reason for encouraging rainwater harvesting.