Civil Engineering June 2021 | Vol 29 No 5

20 June 2021 Civil Engineering Simply, we must understand and respect nature’s economies and limits by reducing wastage, encouraging water efficiency, and promoting a less thirsty economy. But we can also secure our supply without having to exploit ad- ditional water sources – by simply caring for, cleaning, and reusing the freshwater we already have. While water reuse is a logical solution to securing supply of water, it is not simple. And, as it becomes a serious option for water stressed cities, engineers will need to better understand the complexities of how such schemes can be realised. This article outlines the cautious and holistic approach adopted by the City of Cape Town for developing city-scale drinking water reuse schemes in a way that seeks to capitalise on proven techno- logical innovations and build stakeholder partnerships. EMBARKING ON A REUSE JOURNEY Water reuse involves the beneficial use of water sourced from treated wastewater once it has been through an advanced purification process. This can be done at the scale of a single building, a factory, an industry, or even to supplement supply to an entire municipality. The treated wastewater needs to be purified to a standard suitable for its intended use. Factories, warehouses, and commercial buildings often have a significant demand for water that isn’t necessarily of drinking water quality. Alternatively, some cities have very few industrial consumers and the highest demand is from residents who require drinking quality water. It may even be possible to provide consumers with separate water supplies (so-called ‘dual supply’) so that they can prioritise drinking quality water only for uses that require it (drinking, cooking, food preparation, medical, etc.) and use the non-potable supply for everything else. Depending on the proposed scheme, it may be useful to store the purified water for a period in an aquifer, dam or lake (in- direct reuse) or it may be safer to supply the purified water straight to consumers (direct reuse). The primary need in Cape Town is for drinking quality water. After decades of planning and studies, the City of Cape Town has developed detailed plans and the design for a direct potable reuse scheme which would purify treated wastewater to drinking quality and blend RO skid, water reuse demonstration plant, Cape Town (Credit: City of Cape Town) RO system at Goreangab water reuse plant in Windhoek, Namibia (Credit: Wingoc)