34 HEALTH AND SANITATION
Rainwater harvesting guide – background , scope and purpose
South Africa has changed its water legislation to usher in reforms in the water sector and ensure the sustainable use of increasingly scarce water resources .
By
Water Research Commission
While water-related legislations that provide a proper enabling environment for the integrated management of water resources are in place , their implementation still proves to be a challenge .
The South African water experience is unique since , until 1994 , access to water by the vast majority of the population was restricted by the apartheid regime . To convolute the situation further , acid mine drainage from defunct and flooded underground mines severely threaten South Africa ’ s scarce water resources ( Naicker et al ., 2003 ; Hobbs and Cobbing , 2007 ; and Oelofse , 2008 ).
Due to the escalating economic costs of supplying water via centralised supply systems , the ever-increasing demand for water , and the decreasing quality of water bodies , there is a renewed interest in decentralised water supply infrastructures . Rainwater harvesting ( RWH ) is an unconventional water source that has been receiving a lot of attention over the past two decades . In the Sharm El-Sheikh declaration , the African Ministers ’ Council on Water ( AMCOW ), which also includes the South African minister of water affairs , committed to increase RWH ’ s share of total water supply to 10 – 15 %.
Rooftop RWH systems are already a source of drinking water in rural areas ( Figure 1 ), especially in the Eastern Cape and KwaZulu- Natal ( Mwenge Kahinda et al ., 2010 ).
RWH presents many benefits for urban sustainability and is quickly emerging as a key strategy in order to cope with water scarcity in urban and rural South African settlements . The Department of Water and Sanitation supports a national RWH programme , which has a narrow but important focus on the construction of above- and below-ground rainwater storage tanks by rural households for food gardens and other productive water uses . The intention , as highlighted in Chapter 4 of the National Water Resource Strategy 2 ( NWRS 2 ), is to extend the programme to RWH in both rural and urban households and office buildings .
Although RWH is a well-recognised source of water , its nationwide adoption and implementation ( particularly in urban settlements ) have been at a much slower pace . This has been largely due to lack of specific user and programme implementation guidelines .
To develop general or national guidance for RWH , several factors must be considered . While potable use is possible for harvested rainwater , necessary on-site treatment and perceived public health concerns will likely limit the quantity of rainwater used for potable demands . Irrigation and the non-potable uses of water closets , urinals and heating , ventilation , and air conditioning make-up are the end uses that are generally the best match for harvested rainwater . A lesser amount of on-site treatment is required for these uses and , as seen from the usage statistics ( Figure 2 ), these uses constitute a significant portion of residential and commercial demand .
Focusing harvested rainwater on irrigation and selected non-potable indoor uses can significantly lower demand while allowing a balance and a public comfort level between municipal potable water and reused rainwater .
There have been broad suggestions on a project to project basis as to how to ensure optimum quality of harvested rainwater . The Department of Water Affairs and Forestry ( DWAF ) released a document concerning the criteria guidelines required for the design of an RDP rural water supply ( DWAF , 1997 ). Pertaining to RWH , the following were suggested :
• Animals and people should be prevented from contaminating rainwater collection surfaces . House roofs are generally the preferred collection surface .
• Rainwater collection surfaces should be constructed from inert materials and should be well maintained and cleaned ( particularly at the end of the dry season ) to prevent contamination .
• A ‘ first flush ’ system should be incorporated into the rainwater collection system , to remove as much contamination as possible before the storage tank starts to fill .
National RWH guidelines , which give clear direction as to the routine water analysis and monitoring that needs to be undertaken to ensure constant quality of rainwater , do not currently exist in South Africa . This document is therefore a first attempt to address this need .
SCOPE AND PURPOSE OF THE RWH GUIDE Scope The South African rainwater harvesting resource guideline is a manual that provides guidance for the design , installation , and management of domestic rainwater harvesting systems .
Purpose The South African rainwater harvesting guideline is the primary source of information and decisionsupport to all stakeholders . The guidelines contain similar information to what is available in the international literature and a number of guidelines ; however , the information here is tailor-made to South African conditions . The ultimate purpose of the guidelines is to enhance water security by mainstreaming domestic rainwater harvesting into the development and management of water resources in South Africa .
Users of the guidelines The South African rainwater harvesting guidelines are being developed as the primary information resource for stakeholders such as homeowners , engineers , architects ,
November 2017 Volume 23 I Number 9 www . plumbingafrica . co . za