Rainwater harvesting can boost water security

JoJo tankRainwater harvesting (RWH) can boost water security in South Africa, but water-related legislation does not provide a clear legal framework for its adoption, hampering national expansion.

This is according to the Council for Scientific and Industrial Research catchment hydrologist and senior researcher Dr Jean-Marc Mwenge Kahinda, who tells Engineering News that the Department of Water and Sanitation (DWS) should establish a clearly defined national RWH legal framework and produce guidelines using existing knowledge.

RWH involves the small-scale collection, capture and storage of rainwater runoff for various productive purposes, including irrigation, drinking and domestic use. Mwenge Kahinda adds that the legal framework and guidelines should be distributed and enforced using by-laws, with RWH programmes supporting the national framework.

Stellenbosch University vice rector for research and innovation professor Eugene Cloete agrees that RWH should be adopted on a national scale and cites Australia as a good example of its adoption, as the country has legalised RWH in many of its large cities. He notes that, while RWH is commer- cialised in South Africa, the uptake has been slow, owing to the low cost of water in cities and the easy access to this resource.

The DWS’s water services community database indicates that fewer than 1% of households use rainwater as their primary water source for domestic needs, an underuse of RWH.

However, Cloete warns that, if water- shedding becomes a reality, should the country run out of the limited water supply it has, there will be a guaranteed uptake of RWH.


Clear Benefits:

Polyethylene plastic storage tanks manufacturer JoJo Tanks RWH specialist Patrick Rosslee says there has been a year-on-year increase in demand for information on RWH, as well as a surge in the sales of RWH systems.

JoJo Tanks has trained and supports about 40 preferred rainwater installers across the country to keep up with the demand. Rosslee believes that RWH should be adopted nationwide by the industrial, commercial and residential sectors.

“Depending on the internal household use of water, between 30% and 50% of this type of use does not need to be of potable or drinkable quality and, if rainwater was used to replace that water supply, it would reduce municipal water demand by about 30%,” he said.

RWH can be used for irrigation and household use. Under extreme circumstances and with the properly designed system, it can also be used to replace drinkable water.

Rosslee says the quality of rainwater is “relatively unpolluted” and that it is a “soft” water source, which means that, for applications such as washing machines and dishwashers, it is a more effective water source of cleaning, as soaps would sud better.

However, he agrees with Mwenge Kahinda that government should provide clearer national guidelines regarding rebates and connections, which would result in a massive surge in interest and, in turn, a greater roll-out of RWH systems nationwide.

Rosslee adds that RWH could be financially viable if government offered rebates on water tanks and installations. The ‘State of Green Technologies in South Africa’ report, released by the Academy of Science of South Africa (ASSAf) last year, for which Cloete has conducted research, states that the provision of potable water for all South Africans presents a challenge, as there are millions of people without access to a potable water supply. The report cites RWH as one of the solutions to mitigate water scarcity, thereby creating more potable water, with the added advantages of households managing their water directly and water being provided at or near the point of use.

Further, it suggests that RWH could potentially create 1 275 long-term direct employment opportunities and 181 long-term direct manufacturing employment opportunities, Mwenge Kahinda adds that the potential benefits of RWH also include reduced sewage outfall, fewer sewage treatment works and less capital for expensive dam construction, as well as a decrease in demand for new and available water during future water shortages.

While RWH catchment systems are located predominately in private homes and rural areas, 2012 statistics indicated that government had distributed water tanks to the Eastern Cape, Limpopo, KwaZulu-Natal, the Free State and the Western Cape.


Health Hazards?

Although the chemical quality of rainwater is generally acceptable for nonhuman consumption, its microbiological quality does not meet potable standards, says the ASSAf report.

Cloete adds that, as a result, there is a risk of spreading water-related diseases and, therefore, education to avoid water contamination is necessary.

“Generally, harvested rainwater is contaminated with E.coli, faecal coliforms, enterococci and other bacterial pathogens, including legionella. “Depending on the roof type that is used as the catchment area, and amount of chemicals present, including anions and cations, might also exceed the South African drinking-water guidelines.”

He adds that, therefore, research needs to focus on the implementation of point-of-use treatment systems to remove or reduce the level of microbial and chemical contamination.

Pharmaceutical chemistry lecturer Roman Tandlich adds that water and wastewater treatment is often inadequate in rural areas, and that municipal water supply is often interrupted for months at a time.

To remedy this situation, the installation of a rainwater harvesting system can help maintain the potable water supply, he says.


Local Challenges:

Rosslee states that between 30% and 50% of municipal water in South Africa is lost before it reaches the end-user, which he attributes to neglected infrastructure.

The country also has to deal with water pollution challenges that are exacerbated by commercial and industrial water users. There is also a lack of general awareness about where water comes from, how much it costs and how much is available.

Cloete notes that South Africans rely predominately on rivers, dams and underground water sources for their water supply.  The 2011 South African National Census indicated that there are more than 14-million households in South Africa and if they collected only 1 000 ℓ of rainwater collectively, it would make 14-million cubic metres of water available that would otherwise have flowed into rivers.

“In areas that are not serviced by centralised water supply systems, mostly rural and informal settlements, the water challenge is a reality. In most urban areas, however, the water challenge remains a news headline. We are hardly water savvy,” says Mwenge Kahinda.

By: Sashnee Moodley

Edited by: Martin Zhuwakinyu

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