Plumbing Africa February 2018 | Page 27

ENVIRONMENT AND ENERGY informally in many countries. Reuse in peri-urban areas offers an opportunity to produce food close to the area of consumption. POTABLE WATER REUSE The use of treated municipal wastewater for drinking is not quite so common, though well established in some places. The populations of some countries, namely Australia, Namibia, and Singapore, are already drinking treated wastewater, as are some populations in the USA, including in California, Virginia, and New Mexico. It is usually safe, but public opinion is swayed by those who refer to ‘toilet to tap’ reuse as a way to discourage use. Indirect potable reuse (IPR), whereby treated wastewater is added to ground or surface sources (where it receives additional treatment) and eventually ends up as drinking water, has become increasingly common. After tertiary treatment, the water is discharged to a storage reservoir for a period of six months or more. This level of treatment seems to assuage public fears about ‘toilet to tap’ concerns. In reality, a large proportion of treated and untreated wastewater ends up being discharged into a watercourse and used downstream as a water supply. NON-POTABLE REUSE: INDUSTRIAL, COMMERCIAL, RECREATIONAL, AND PERI-URBAN AGRICULTURE Local reuse becomes more economically feasible if the point of reuse is close to the point of production. Many industrial and commercial establishments are in need of process water, and can institute better housekeeping procedures to reduce their dependence on water consumption and wastewater production, as well as the associated costs. Businesses can directly reuse some untreated wastewater, provided it is of adequate quality. Good sources include process water for cooling or heating, and rainwater from industrial/commercial roof collection or airport aprons and runways. Industrial symbiosis is often used to describe partnerships and cooperation between two or more different industries to enhance both environmental performance and competitive capacity by exchanging and optimising mutual material, energy, and water flows. In the case of water reuse, this occurs often at a local scale. By-products of one industry become feedstocks in another. Similarly, process cooling water may be used for heat recovery or for productive use. Sometimes, partnerships share the management of utilities or ancillary services. The United States Environmental Protection Agency (US EPA) gives a good account of urban reuse systems that provide partially treated (fit-for-purpose) wastewater for www.plumbingafrica.co.za 25 various non-potable purposes, including irrigation of public parks and recreation centres, athletic fields, school yards and playing fields, highway medians and shoulders, and landscaped areas surrounding public buildings and facilities; irrigation of landscaped areas surrounding single- family and multi-family residences, general washdown, and other maintenance activities; irrigation of landscaped areas surrounding commercial, office, and industrial developments; irrigation of golf courses; commercial uses, such as vehicle washing facilities, laundry facilities, window washing, and mixing water for pesticides, herbicides, and liquid fertilisers; and ornamental landscape uses and decorative water features, such as fountains, reflecting pools, and waterfalls. In dual distribution systems, the partially treated wastewater is delivered to customers through a parallel network of distribution pipes separate from the community’s potable water distribution system. The reclaimed water distribution system becomes a third water utility, in addition to wastewater and potable water. Reclaimed water systems are operated, maintained, and managed in a way that is similar to the potable water system. Direct use of treated municipal wastewater has been practised for some time. Supplying nutritionally adequate and safe food to city dwellers poses a substantial challenge. Peri-urban agriculture offers one solution but requires adequate water. Municipal wastewater is often (usually informally) used without treatment, resulting in serious health risks for both farmers and those who consume the food. Social customs and diets dictate how risky this practice is. MANAGING URBAN RUN-OFF Climate change adaptation seeks to lower the flood risks associated with extreme rain events, but if developed in synergy with urban development, it can also address some of the problems associated with urban wastewater management. Cities are increasingly concerned with the effects of climate change, which include higher risks of flooding and raised temperatures, combined with increasing demands for safe drinking water supplies. Rainwater in the form of surface runoff can contribute to cities’ water balance and be collected to create attractive recreational areas. PA It is better to restrict the discharge of hazardous substances to sewers, particularly those that render the wastewater difficult to treat. February 2018 Volume 23 I Number 12