The health impact of microplastics - bits of plastic less than 5mms in size - that were found in tap water in Johannesburg and Tshwane is at this stage unknown, Rand Water has said.
This comes as a new study reported that substantial amounts of microplastics were found in the tap water supplied to both cities, as well as in rivers in Gauteng and in borehole water in the North West.
"We have been monitoring the global trends and findings around microplastics in water," said Rand Water spokesperson Justice Mohale.
"In this respect, we have proactively established an initiative to investigate microplastics. While doing so, it should be noted that knowledge of microplastic contaminants in drinking water is in its infancy; and guidelines/standards for drinking water are yet to be established."
The study - one of the first to assess the level of microplastic pollution in South Africa's fresh water - was commissioned by the Water Research Commission and carried out by researchers at North-West University.
Rand Water supplies water to more than 15 million people in Gauteng and surrounding provinces.
It said microplastic pollution had been gaining momentum as a global environmental concern.
Rand Water welcomed the results of the latest study, noting that the findings were consistent with research in other countries.
"These studies will assist with the ongoing monitoring and management of microplastics in water bodies and drinking water," said Mohale.
He said Rand Water subscribes to legislative requirements that the water supplied complies with South African national drinking water standards.
"In addition, we have implemented a water quality management system in line with the global best practice 'Water Safety Plan'.
"This best practice was established by the World Health Organisation and International Water Association," he said.