DWS
of reusing water is becoming increasingly competitive with the traditional supply alternatives and this will be a key driver for increasing reuse of water in future .
The typical increasing cost of different water sources is reflected conceptually in Figure 2 . Water reuse must be considered as one of several options to augment water supply to a city , industry or mine , once the conventional fresh water resources are fully developed or the cost of water reuse becomes comparable to the development of conventional water sources .
The economic value / cost of water must also be seen in the broader context of affordability , reliability , and responsible use of a limited resource .
Figure 2 : Comparative cost of different water sources .
Therefore , considerable potential exists to substantially expand the use of treated wastewater for irrigation purposes in South Africa . This will bring many benefits . Irrigation is often labour intensive and expanding the area under irrigation may create jobs . Wastewater return flows are typically available close to urban areas and thus close to urban markets for agricultural produce , provided suitable land is available for irrigation .
Treated wastewater can substitute for freshwater , thus making more freshwater available for other uses .
Any such reuse of water by agriculture will have to be balanced by other competing requirements and historical allocations of water in the specific water management area .
Municipal sector : non-potable water
The main source of water for reuse in municipal ( urban ) areas is wastewater from municipal treatment works . This typically comprises a mix of domestic sewage and other wastewater . Other sources of water for reuse include grey water ( usually available at the household / water user level only ) and industrial effluents .
The main potential uses of treated wastewater from municipal wastewater treatment works is for the irrigation of public open spaces ( like parks ), sports fields ( municipal , schools , and clubs ), golf courses , and cooling ( related to industry and power generation ). The return flows from wastewater treatment works can also be important for urban water systems ( rivers , lakes , dams , and wetlands ).
Treated wastewater and / or grey water can also be used for firefighting , toilet flushing , cooling systems , street cleaning , dust control , and a variety of applications that do not require potable water .
Of the total volume of municipal wastewater treated , it is estimated that only a small fraction is reused ; most of it is for the irrigation of public open spaces , sports fields , golf courses , and cooling systems . In the past , the urban / municipal reuse of treated wastewater was not actively promoted due to the cost of such systems and the potential public health risks . Some reuse of water , for example in the irrigation of recreational areas and golf courses , may be in competition with other essential water uses .
Municipal sector : potable water
Used water can be treated to a standard that is fit for domestic use ( drinking purposes ). Treated water can be supplied directly to households ( direct reuse ) or be discharged back to the ( fresh ) water resource where it is blended with other water and subsequently abstracted , treated , and distributed for use ( indirect reuse ).
The majority of these schemes are based on an indirect reuse approach . Indirect water reuse for potable purposes is well established in South Africa . It is common for a treated wastewater effluent to be discharged to a river system and for water to be abstracted downstream of this discharge point and to be treated and used for drinking water . The direct reuse of used water for potable purposes has not been implemented in South Africa , but has been successfully implemented in Windhoek , Namibia , since the 1970s . u
There are many potable water reuse schemes in operation in the world . networking contributor industry debate environment infrastructure municipalities
Water Sewage & Effluent May / June 2017 21