The Democratic Alliance (DA) says it will open a criminal case against City of Tshwane officials over alleged failures to warn residents about potentially unsafe drinking water in Bronkhorstspruit.

The announcement follows reports of between 140 and 160 cases of diarrhoea and other gastrointestinal illnesses in Bronkhorstspruit and surrounding communities earlier this month.

DA Tshwane mayoral candidate Cilliers Brink said the party had received information from a whistleblower alleging that the Bronkhorstspruit Water Treatment Plant had operated without chlorine treatment for three weeks.

Brink said the DA would request a criminal investigation into whether municipal officials had failed to comply with their legal obligations to warn residents of potential health risks.

The party has also demanded that Mayor Nasiphi Moya explain when she became aware of problems at the plant and whether she knew that chlorine treatment had allegedly stopped.

The DA wants the immediate publication of water-quality test results, chlorine treatment records, and operational reports.

The treatment plant has faced longstanding operational difficulties and is operating well below its capacity.

The City of Tshwane has confirmed that it is investigating the outbreak and has intensified water testing across the affected distribution network.

Most patients were treated at Bronkhorstspruit Hospital, with others receiving treatment at hospitals in Pretoria. No deaths have been reported.

Residents have been encouraged to use alternative safe water supplies, including municipal water tankers sourcing water from Cullinan, while investigations continue.

The planned criminal case comes less than three weeks before the 4 November local government elections, in which control of Tshwane is expected to be closely contested.