South Africa’s groundwater, on which nearly two-thirds of South Africa depends solely or partially for domestic use, needs to be used wisely, said University of the Free State Institute for Groundwater Studies director and geohydrologist Dr Eelco Lukas.

Groundwater, a significant source of water and in some parts of the country the only source of potable water, is becoming increasingly important in the water-stressed country, and can be found almost everywhere.

“But that does not mean that we can start pumping groundwater at any location,” he explained, noting that in many places, the amount of groundwater available is so little, or the water so deep, that it is not financially viable to pump it, and the quality might pose a challenge.

Numerous towns and communities depend solely on groundwater through boreholes and many towns use a combined supply of surface and groundwater.

“However, problems can arise when a borehole is drilled for a community with a certain number of people and soon there are many more people than the borehole can supply. It is not so much a case of the borehole drying up but that the capacity was exceeded.”

Groundwater sustainability is dependent on demand and supply, both of which are beyond the control of the geohydrologist.

“When enough water is available for a community, the chances are that the community starts to grow, thereby enlarging the demand.

“If the higher demand cannot be met, sustainability is no longer possible. When a change in rainfall pattern results in a decline of the precipitation, the groundwater recharge will become less resulting in a lower supply of water,” Lukas explained.

The most recent estimate of sustainable potential yield of groundwater resources at high assurance is 7 500-million cubic metres a year, while current groundwater use is estimated at around 2000-million cubic metres a year, he said, citing data from the Department of Water Affairs and Sanitation.

“Allowing for an underestimation on groundwater use, about 3 500-million cubic metres a year could be available for further development. Unfortunately, if there is a shortage of water on one side of the country it cannot be supplemented with water from the other side.”

Further, during a drought, with below-average rainfall, the available water to recharge is also less, leading to declining groundwater levels.

Groundwater users will also pump more water to make up the deficit in rainfall, thereby accelerating the drop in water levels.

However, the pore space in aquifers can be used to store water during a wet period, to be used later during a drought.

“This is called water banking where water is injected into the aquifers (artificial recharge) during a period when there is enough water and pumped from the same aquifer during a period of water shortage,” said Lukas.