Reduced water availability, owing to the current drought conditions and one of the driest rainy seasons, have resulted in many households and companies having to deal with the reality of water insecurity. This has led to increased searches for and securing alternative water sources, such as domestic rainwater harvesting (DRWH), Water Research Commission (WRC) research and development group executive Dr Stanley Liphadzi tells Engineering News.
RWH involves collecting, channelling and storing water runoff from different surfaces for household consumption, livestock and food production.
“Increased community and domestic households’ efforts focus on harvesting rainwater from rooftops, in-field, pavements and roads in the urban, periurban and rural areas, thereby resulting in a mushrooming of water tanks in many areas,” Liphadzi says.
He believes that reduced water availability at source, and in dams and reservoirs is a key motivation for using DRWH.
To date, the current drought has also adversely affected water supply, agriculture, as well as food and production prices.
Polyethylene plastic storage tanks specialist JoJo Tanks manufactures a broad range of polyethylene water storage tanks. The company’s RWH specialist, Ettienne van der Merwe, tells Engineering News that the potential of DRWH systems is underscored by the increasing number of such installations, as well as requests for information on the systems.
Product interest steadily increased throughout 2015, with demand peaking in October, he highlights.
JoJo Tanks MD Grant Neser adds that DRWH demand from residential and commercial properties in urban markets increased at least threefold in late 2015, compared with historical demand. This is particularly the case in Gauteng, following water availability issues in the last quarter of 2015. Demand in the Free State and KwaZulu-Natal – which face severe water stress and have been declared disaster areas – has also increased.
He expects that heightened demand for the systems will continue this year, with JoJo Tanks and fellow industry players currently under pressure to produce enough water storage tanks to meet demand for domestic use.
Further, more households and industries are considering DRWH systems, as water tariff hikes, as well as the subsequent reliability, quality and quantity of water could also become a reality.
Van der Merwe points out that, for every 1 m2 projected roof surface that receives 1 mm of rainfall, 1 ℓ of water can potentially be collected. A city house with a 150 m2 roof surface that receives 10 mm of rain can collect 1 500 ℓ of rainfall.
“During a decent shower, a company can easily harvest 100 000 ℓ in an hour from an industrial or warehouse-sized roof, for example,” he suggests.
Although DRWH systems manufacturers claim that using rainwater can reduce municipal water demand by 30% to 40%, Council for Scientific and Industrial Research (CSIR) catchment hydrologist and senior researcher Dr Jean-Marc Mwenge Kahinda indicates that there are no observed data to validate and verify the outputs of existing DRWH models and, therefore, assess their reliability.
“Various DRWH models produce different outputs, tank sizes and water savings for the same input parameters, rainfall and demand. It is, therefore, impossible to decide which results are accurate without observations,” he warns.
The CSIR is consequently conducting a study, titled Water Security in South Africa: Tools to Promote Reliable Water Supply in the Domestic and Agricultural Sector. It currently includes the monitoring of rainfall, tank levels and water use at four different DRWH systems: two at the CSIR, in Pretoria; one at the University of the Witwatersrand; in Johannesburg; and another at the Enkanini informal settlement, near Stellenbosch, in the Western Cape.
A key aim is to generate sufficient data to optimise DRWH systems in distinct rainfall areas of the country using validated DRWH models. The study will also provide estimated return-on-investment (ROI) periods for the systems.
Other focus areas of the study include the quality of harvested water and subsequent health impacts of its use. Several studies have focused on the bacterial content of rainwater, which include E.coli, faecal coliforms, legionella, enterococci, bacterial pathogens and other chemicals; this study will focus on viruses.
The WRC is in the final stages of a project where the health risks of rainwater harvested from rooftops and stored in tanks for domestic and livestock use in rural villages are being analysed. The results will be published by the end of this year.
“It can be argued that, as a result of lower rainfall, the potential contamination of rooftop-harvested rainwater can increase, owing to a higher concentration of contaminants,” Liphadzi says, but adds that this has not been scientifically verified.
The respective findings from these studies can provide key information to assist in rolling out a sizable DRWH government programme, with support for a coordinated, DRWH mainstream approach within the country’s water resources strategy, Mwenge Kahinda suggests.
Mwenge Kahinda, however, adds that the influence of a nationwide implementation of DRWH systems should be investigated, particularly regarding the business or cost impacts for large water utilities and municipal water providers.
“The effects of either a significant or marginal reduction in water required from municipal water sources, such as dams, as well as a potential reduction in water received by wastewater treatment works, are, however, yet to be determined,” he acknowledges.
Since 2007, government has, on a smaller scale, distributed DRWH systems and storage tanks to rural areas.
Mwenge Kahinda reaffirms the prevailing need for a clear, enabling environment, suitable legislation, a national body comprising “foot soldiers” to oversee and ensure the proper implementation and regulation of DRWH, as well as the need for a national DRWH strategy.
Despite broad agreement that government should provide clearer national guidelines regarding rebates and connections, which could result in increased interest in and greater roll-out of DRWH systems nationwide, he notes that DRWH is yet to be mainstreamed into the country’s current water resource assessments.
“Industry still needs a policy position paper from the Department of Water and Sanitation to clarify current uncertainties of DRWH in water-related legislation,” Mwenge Kahinda says.
He stresses that the fast-tracked, mass roll-out of DRWH systems could curtail demand for or lead to a delay in the expansion of new water- related megaprojects and infrastructure.
Although DRWH is neither a silver bullet nor the only sustainable solution to ensure the country’s water security, Liphadzi, Van der Merwe and Mwenge Kahinda believe that DRWH should be implemented as an integrated solution to support municipal supply.
Neser agrees, stressing that DRWH systems cannot replace municipal supply in its entirety. “Rainfall over most of our country is infrequent and of high intensity, requiring large amounts of storage capacity to be effective. One of the main challenges with RWH is the effective use of water after a rainfall event to create storage capacity for the next event,” he points out.
Liphadzi believes the method remains a multiple catalyst “with vast potential to dramatically increase household water security, while reducing the strain on drinking-quality water in the urban environment”.
It can also become a genuine enabler of local socioeconomic development in the rural environment and, by implication, improve food security.
“When combined with smart energy solutions, such as solar and biogas, there is a chance to remove a core constraint to a higher quality of life through universal access to vital services, such as water and energy,” he argues.
Liphadzi suggests that diversifying supply options and developing new water infrastructure must go hand in hand with more efficient individual use to reduce demand.
“DRWH, as a supplementary water source, has greater potential along the east and west coasts of South Africa, as it rains there throughout the year. However, inland areas have fewer months of rainfall – hence, the storage requirements . . . can be quite large,” he says.
Van der Merwe also believes that DRWH systems are a complementary and viable alternative to large-scale water withdrawals, highlighting the availability of dual-water supply and management systems that can provide significant advantages.
However, the success and usefulness of DRWH depends on a constructive use of the harvested supply and not on long-term, ineffectual storage, he says.
Van der Merwe adds that current constraints for DRWH success include justifying the capital outlay to install a well-designed and fully functional DRWH system.
The ROI period for most systems at current water tariffs ranges from four to five years. “These tariffs consequently provide no real compelling argument for a DRWH system with a significant financial return,” he says.
Wits School of Governance visiting adjunct professor and former Department of Water Affairs director-general Mike Muller says such dual-infrastructure systems could be considered, but warns that DRWH will not make a significant contribution to South Africa’s water challenges.
The most important rainwater harvesting we do is capturing river flows in our dams. In years of drought, household RWH has less potential, “as it doesn’t solve long-term drought or mitigate significant water interruptions”.
Most domestic RWH systems store less than 10 000 ℓ – usually not enough to supply a household for more than a few weeks, Muller argues.
Demand for municipal water infrastructure will continue and increased capacity will be required to ensure urban water security, he concludes.