Illegal or poorly preserved private sludge and rainwater pipes are accused of the large amount of human waste polluting Auckland beaches.
Wastewater overflow is an ongoing problem for the city and the Auckland DNA Council has tested about 20 beaches known to have water quality problems over the last four years.
Approximately 650 samples were taken and more than half showed human infection.
The aging of the wastewater infrastructure has been accused of overflowing in the past, but Anne Nama of Watercare said it was wrong.
"The sources we have identified so far tend to be mainly related to people who have interconnected their waste water with the rainwater, with private pipelines that tend to fail and leak over time," he said.
"We have nothing to show that Watercare's infrastructure is inadequate."
Mr Nama said that their findings from Takapuna Beach are a good example.
"We have identified a toilet block in their private pipelines … actually absorbing the sewage and entering the rainwater system and then on the beach," he said.
"You know that the positive result identified by Takapuna was a direct result of poor private infrastructure and not the aging of the Watercare infrastructure."
He said that people who remove fats, oils or rocks in sewer systems also cause jams.
And this can lead to overflow problems.
"If we continue to say," This is a Watercare issue, it's a Watercare issue, "we will not solve the problem," he said.
"[The] the majority of the problem will be related to things that do not have to enter our network that enters our network of people who put things down. "
Nikos Vigar of the council's Safeswim branch, who is examining the water test, encouraged anyone suspected of leaking pipelines to come in contact.
"There is a fair expense in trying to identify these problems," he said.
"We are more than happy if people come to us and say" look, we think there is a problem, "we will be helping and resolving this issue with them."
Mr. Vigar said the public should make sure they check the Safeswim website, which shows the quality of the beaches' waters before they swim.
He said the council has worked hard on identifying and defining sewage issues, but it would not be a quick fix.