Civil Engineering June 2021 | Vol 29 No 5

Civil Engineering June 2021 25 last. In this sense, dams are like a house- hold’s bank account. If wages are paid into the account once a month, the family needs to plan how to spend it so that it does not run out. If the flow of money reduces, so too must expenditure. Dams work the same way. The water deposited in the reservoir is like the wages paid into the bank – users must make sure that it does not flow out so fast that there is none left before the next rains arrive. Enough must be kept in reserve in case there is a dry year. So, two factors must be considered together to avoid water crises: technical matters like rainfall, river flow and infrastructure; and human factors like the behaviour of water managers and users. South Africa’s climate is relatively well documented. The priority for water planners is to manage the fact that rainfall is highly variable. Planners work with hydrologists and climate scientists to estimate the risk that there will be a succession of dry years. They calculate how low river flows will go and how much storage is needed to keep supplies running. That kind of information, used to plan the infrastructure of the IVRS, has kept the region water secure for almost 40 years. It also flagged the need to build the next phase of the LHWP. That is where the human factors intervene. To meet the water needs of populations and economies, planned investments must be made on time. And until additional supply is available, water use must be kept within safe limits. This requires water users to change their behaviour. HUMAN BEHAVIOUR Since the Gauteng population is growing at about 3% per year, and supply is fixed, consumption will have to decrease by 3% per year if the region is to remain water secure. But if people see full dams, can they be persuaded to reduce their water use? Some efforts are already being made. Rand Water has a critical role to play and has reached the limit of what it is allowed to take from the system. The water utility is now rationing available water between its different users. Consumption targets have been set for individual municipalities and Rand Water is restricting supplies to those that don’t use their water efficiently. Consumption per person in the region is around 300 ℓ per day – well above global averages – so there is room for improvement. In addi- tion, almost 40% of the water supplied to municipalities is non-revenue water – water either lost through leaks or not billed and paid for, and thus often wasted. At the root of these problems is poor management and maintenance. To cope with supply restrictions, mu- nicipalities face difficult choices. Most are trying to reduce their non-revenue water. Some are delaying new housing and in- dustrial developments. Others are cutting supply to selected suburbs for days at a time when they reach their allocated limit. The region’s citizens have not yet been told the hard truth that for the next six years, this supply squeeze will get tighter. Yet this information is essential if communities and households are to play their part. People will not change their behaviour unless they are told what is happening and how to avoid a crisis. GOING FORWARD A lesson from Cape Town’s Day Zero experience was that when people were told about the problems, and about how the city and their neighbourhoods were performing, they reduced their water use. Cape Town showed that people will take difficult actions when there is a problem they can see and understand. It has been suggested that Rand Water should publish monthly reports on the pro- gress made to achieve municipal savings targets. That is politically delicate since national ministers are reluctant to expose their local counterparts to criticism. So, the technical dimension of en- suring reliable water supply – managing the dams, treatment works, pumps and pipes – is difficult. But even more chal- lenging is the task of motivating human interventions, from ministers down to households. The measure of success or failure is whether the water comes out of the taps when needed. And too often, it is human behaviour rather than infrastructure that fails us.  The article was originally published on This Conversation under a Creative Commons license. South Africa