Information on hundreds of dysfunctional sewage treatment plants will not be made public, the government said on Wednesday.

In a written reply to Parliamentary questions, Water and Environmental Affairs Minister Buyelwa Sonjica said that revealing such information could lead to "serious misinterpretation" of the data.

"What is available and was published... in the 2009 Green Drop Report, is the summary of the performance of each of the 449 WWTWs [waste water treatment works] that were assessed," she said.

The Green Drop Report - an audit of 449 of South Africa's 852 municipal WWTWs, conducted between August 2008 and July 2009 - was released, after long delays, in April this year.

According to the document, a total of 403 facilities were not assessed owing to, among others, "municipal officials not sufficiently confident in their levels of competence" and "municipalities not managing waste water services according to expected requirements".

It also found that of the 449 works that were assessed, skills shortages had resulted in many not being operated correctly and "the effluent water quality is no longer compliant".

Among the Parliamentary questions posed to Sonjica - by Democratic Alliance (DA) MP Annette Lovemore - was whether information for all WWTWs would be made available to the public, and if not, why not.

The Minister replied: "No, such detail [sic] information is not available to the public. Revealing details of such a high technical nature will lead to unnecessary additional administrative challenges and serious misinterpretation."

Speaking to Sapa, Lovemore said that not making public information on potential threats to people's health was unacceptable.

"It's not acceptable. Each municipality is required to report on results [from WWTWs] each month. If there is a health risk, people should be told."

She said that over and above the risks to human health of sewage water finding its way into rivers and streams, the contaminated water also affected crop irrigation, drinking water for livestock and the health of the environment.

In her reply, Sonjica further said that not all WWTWs had been issued licenses or permits to operate. She did not say how many.

Reasons for municipal sewage works not having operating licenses included that some had not applied for one, some did not meet the standard required for a license, and others had "insufficient capacity" to submit the application.

Her department had launched a special project "to address the current backlog in licences", she said.