Rainwater Harvesting: Why, What and How

Environmental Scientist Zoë Gebhardt tells us more about rainwater harvesting.
 
Why South Africa is a water stressed country
 
With the recent implementation of Stage 2 water restrictions in Johannesburg, most South Africans are now aware that our country is facing one of the worst droughts since 1992. In 2012, South Africa was identified by the United Nations as a physically water scarce country, meaning our water supply could no longer meet our water demand. Unlike many other cities around the world, our cities were built around mining and not existing water resources. This meant that as the population grew and demand increased, water needed to be pumped great distances to meet increasing demand. For Gauteng, this ultimately resulted in the Lesotho Highlands Water Project, which is the largest water transfer scheme in Africa.

With an average of 464mm of rainfall per year, South Africa’s average yearly rainfall is about half the global average of 860mm. This, coupled with the current El Niño conditions, a weather phenomenon that rapidly heats the Pacific Ocean and brings drought to the southern hemisphere, could see South Africa being five to seven years away from the “wet period” rainfall we so desperately need.
 
What is rainwater harvesting?
 
In light of this, it seems only appropriate that we further explore practical ways in which all South Africans can learn to rely less on piped municipal water and start to rely more on sustainable water supply options, such as rainwater harvesting. Rainwater harvesting has been undertaken successfully throughout Africa and can be implemented cost effectively by residents of high, medium and low income areas. Rainwater harvesting essentially involves the collection, storage and continuous use of captured rainwater, as either a main or alternative source of water.

There are a number of rainwater harvesting projects in South Africa namely: Botlhabela Village Project in Alexandra, Johannesburg; the Cato Manor Green Initiative in Durban and the Indlovu Centre in Khayelitsha, Cape Town. Collectively, these projects assist in supplementing water supply and management in low income communities, as well as improving their quality of life.
 
How can rainwater harvesting systems be implemented?
 
In order for the water to be potable (drinkable), the right materials need to be used to construct the harvesting system and is important that these materials are simple, affordable and easy to acquire. Recommended materials for roofing include galvanised or corrugated iron sheets and corrugated plastic or tiles. Gutters can be made of local materials such as metal, aluminium or PVC whilst storage tanks can be made from plastic, bricks, cement, concrete or reinforced concrete.

It is important for harvested rainwater to be filtered, especially if it is going to be used as drinking water or for domestic purposes. Course and finer mesh filters should be spaced along the gutters and pipe connections in order to filter the collected water before it reaches the storage tank. The finer mesh filters should be placed closer to the storage tank.
 
Conclusion
 
Effective rainwater harvesting has multiple benefits for low income areas such as enabling households to save money, which would otherwise have been used to pay for water supply from municipal agents; as well as enabling households to save time and resources, which would otherwise have been used to search for water for domestic use. Saved money, time and resources can then be diverted to other productive uses such as farming, trading and schooling. Stored rainwater may also assist in reducing the onset and spread of certain diseases associated with poor water and sanitation practices. Rainwater harvesting therefore assists in promoting the health and wellbeing of households, while collectively reducing pressure on municipal water supply.

 
Thank you to Ms J.P. Enninful (WITS) for her 2013 paper on Rainwater Harvesting, which helped inform this article.

 
Joint Aid Management South Africa is fundraising for a water collection tank which will be installed at the Phakamani Preschool. The water collected will be used as an additional source of drinking water, and also to water the vegetable garden. Go here if you’d like to contribute.