Civil Engineering October 2022 | Vol 30 No 9

18 October 2022 Civil Engineering I ntermittent water supply is usually associated with either an unforeseen crisis event or simply the water service provider being unable to maintain a proper and reliable water supply due to a variety of reasons such as lack of budget or simply poor management. South Africa’s main water supply systems have been reasonably reliable in the past and intermittent water supply in major urban centres has been the excep- tion rather than the rule. In more recent years, however, there has been a worrying trend in some areas where intermittent water supply is being used on a regular basis to control water demand or to reduce water losses from municipal water supply systems. “Day-zero” drought events are be- coming more frequent across the whole of Southern Africa due to a combination of increasing urban populations as well as the impacts of global warming which exacerbate the natural flood and drought sequences that the various regions must expect due to their normal climatic condi- tions. Droughts will become more severe and last longer while floods will be more destructive and increase in frequency. Both floods and droughts can have a very sig- nificant impact on water supply and cause water shortages which in turn can force water service providers to introduce “water shedding” which in effect is the practice of introducing intermittent water supply. In some instances water suppliers are resorting to intermittent water supply in an attempt to reduce water losses and/ or normal consumption. In other areas such as parts of KwaZulu-Natal the water infrastructure has been damaged by exceptional floods to such an extent that there is simply no alternative in the short term. In both situations, it is important to appreciate the potential dangers of intermittent water supply and to try and restore a full pressurised water supply as soon as possible. This article tries to highlight the po- tential implications of intermittent water supply and shows that although some savings can initially be achieved through the introduction of intermittent water supply, in the long-term, such measures will often result in higher water use. The article will also highlight the possible health issues that must be considered where intermittent water supply is being used as a measure to control or reduce water demand. SETTING THE SCENE The supply of safe drinking water is be- coming one of the most important issues in the 21 st century and despite the efforts to provide a safe supply to the world’s population, the situation is not improving. In fact, in many parts of the world it is de- teriorating. A growing population, global warming, improved living standards, and land use changes are among the many factors which exacerbate the impacts of normal flood and drought events. Climate change is often blamed for the droughts and floods which appear to be becoming more severe than previously recorded events. Floods and droughts are natural events which are caused by climatic variability, and they must be expected with or without the added impact of climate change. Population growth and land use changes also have a significant impact on available water resources and climate change adds to the pain and creates droughts that are more severe and last longer than would otherwise be expected. Droughts are often also “broken” with flood events which can be so severe that they create huge problems to the water re- source infrastructure and ironically create water shortages due to the damage they cause. The situation is unlikely to improve and will most likely deteriorate. Water supply managers and other government officials must prepare for more extreme and damaging events in future. When considering potable water supply, South Africa has many different issues to deal with. By global standards, the country has relatively efficient reticulation systems in most of the metros and large municipalities where tap water is generally safe to drink and water is typically supplied at normal first world pressures 24 hours a day. While this is often taken for granted in many parts of South Africa, it is unusual in most parts of the developing world. Inversely, many of the country’s rural areas regularly experi- ence severe supply problems during times of drought, and in the case of KwaZulu- Natal now also in times of flood. Large integrated water resource schemes tend to have greater resilience Dr Ronnie Mckenzie Pr Eng, FSAICE Water Loss Specialist: WRP Past Chairman of the International Water Association: Water Loss Specialist Group ronniem@wrp.co.za The dangers of intermittent supply in South Africa In many countries around the world, especially in Asia and parts of Africa, intermittent water supply is a way of life and residents often have to deal with a water supply which is only pressurised for a few hours a day or even a few hours per week. Such intermittent water supply causes huge problems in the long-term viability of water reticulation systems and poses significant health risks. There has been a worrying trend in some areas where intermittent water supply is being used on a regular basis to control water demand or to reduce water losses