Keep calm and save water

As the levels in Cape Town’s major storage dams decline, the number of “bangmaakstories” (scare stories), increases proportionately. Social media channels are littered with dire predictions of a dystopian world in which our water supply simply dries up, and we have nothing coming out of our taps.

One such prediction suggests that Cape Town has 12 weeks – 84 days – of water left at current consumption levels, and assuming no recharge from rain or any other source. That puts the deadline for our taps running dry at April 10.

The City of Cape Town’s water dashboard shows that consumption sticks stubbornly above the target 800 mega litres (ML), currently 890ML a day, despite Herculean efforts to bring it down.

Referred to as demand management, these efforts attempt to persuade, cajole and eventually coerce consumers into using less water.

According to Dr Keith Kennedy of the Council for Scientifc and Industrial Research (CSIR) water research division in Stellenbosch, the “days of water left figure” is something of a moving target, because it depends on the variables that are taken into consideration when the calculation is made.

Using figures from the City as at January 16, and premised upon the following assumptions – daily consumption of 890ML, 898 221ML storage volume, 15% of storage volume difficult to get out and distributed to users, no recharge from rain or any other source – we have 278 days of water left, and that takes us to October 21 before the taps run dry, assuming that nothing changes.

But as the City’s manager bulk water, water and sanitation, Barry Wood, pointed out in a radio interview last week on Wednesday: “The dams are not going to run empty before the onset of the winter rains, like people might be saying. The demand is a combination of urban and agricultural. The City gets its water from a collection of dams where there are other users involved, such as agriculture and other municipalities.”

He went on to say that as temperatures cool over the next two months, agricultural demand will decline, and he expressed the hope that urban users would comply with the current Level 3 water restrictions to get daily usage down to the target 800ML.

“Our view is that the dams will probably drop to around 20% by the end of summer, and our concern is not so much for now, but it is for next summer,” he said. “These dams take between one and three years to fill, depending on their size.”

“We don’t know what the weather holds going forward. We might get good rains, but if the rains are not good this winter, then we’re just going to tighten up on restrictions,” he says. “That is the only way we can manage it in the short term.” The imposition of Level 3b water restrictions (see sidebar) will, in all likelihood, be adopted at the City’s council meeting tomorrow.

Astronomically speaking, the “end of summer” is the Spring Equinox, March 20, the date beyond which we would hope that rain begins to fall. If dam levels are at 20% by that date it is frighteningly close to the 15% level at which extraction becomes difficult, and a long way from October 21, but as Dr Kennedy points out, his estimate does not take into consideration draw downs by agriculture, other municipalities, or losses due to evaporation of the volumes at the major dams.

In tandem with the fear-mongering about imminent water shedding, come the myths propagated around the use of desalination, and the exploitation of groundwater, neither of which provide a short term solution to our drought-induced, regional water shortage.

Desalination as a source of potable water, is not a top priority for the City of Cape Town. It is expensive, in capital, energy, and operating cost terms and the brine which results from the process must be disposed of.

Groundwater on the other hand, does offer a potential source of supply, according to Umvoto Africa research and technical director, Dr Chris Hartnady, who is leading an investigation for the City of Cape Town, into the feasibility of exploiting groundwater from the Table Mountain Group Aquifers (TMGA).

Speaking on the same show as the City’s Barry Wood, Dr Hartnady dispensed with the myth that the “Table Mountain Aquifer” has anything to do with Table Mountain, pointing out that the TMGA is an enormous geological formation, which extends from just east of Port Elizabeth, across the Eastern, Southern and Western Cape coastal regions to the Cape Peninsula, then North up the West Coast to Nuwerus.

The TMGA is not easily exploitable, and Dr Hartnady’s research study is focused on determining the feasibility of exploiting it economically and sustainably. According to Dr Hartnady, the bulk of the exploitable water resource in the TMGA, is “essentially underneath a lot of the dams.” Whereas we currently get about 400 million m3 of water a year from the dams, there are billions of cubic metres in storage in the TMGA. His research indicates that the area most suitable for exploiting the TMGA, is in the vicinity of Theewaterkloof.

The next phase will see test wells drilled there to determine if it can be accessed economically, and managed sustainably, so that “damage is not done to perennial flows” according to Dr Hartnady, and the earliest that the TMGA could be commercially exploitable, if the testing and monitoring goes according to plan, is 2024.

In the meantime, according to Mr Wood, the Voëlvlei augmentation scheme, which will see water pumped from the Berg River into the Voëlvei Dam in winter when the Berg Dam is full, will be in place by 2021.

By 2023, the City will be recycling wastewater back to drinking water standard, generating about 100ML per day.

Until these new sources of water come on stream, or sufficient rain falls, it is vital that consumption is reduced to levels that will make what water resources we do have, last.

Next week: What can you do to save water?