A small number of water suppliers are dealing with contaminated water problems through band-aid solutions, according to the authors of a study on failing drinking water standards.

The report, Failing the Drinking-Water Standards – Insights from the Annual Survey, was presented to the Water New Zealand Annual Conference in Rotorua this week.

ESR Science leader Dr Chris Nokes says the vast majority of New Zealand communities have access to good quality water.

But a review of annual survey data reveals more than 10 per cent of water supply sub-areas, which serve more than 500 people in 2013/14, failed to meet the Drinking Water Standards because E. coli was detected on too many occasions, or there was inadequate monitoring.

A little more than a quarter of these zones had failed in at least three of the four previous years because of the detection of E. coli.

Chris stresses these results don't necessarily mean the water was unsafe, but the presence of E. coli indicates faecal contamination of the water so further investigation is needed.

It's important to find out the cause of the contamination, especially when there are repeated cases of failure, says Chris.

'Intermittent, low levels of E. coli contamination can be difficult to investigate.”

'In circumstances where there have been a high number of transgressions, or failure to meet the standards, the cause could be an ongoing problem needing attention, such as inadequate treatment or contaminants entering the water after treatment.”

Temporary chlorination is often used to provide a short term solution, but does not address underlying issues.

Chris believes all water suppliers should be encouraged to permanently treat water with chlorine and, where necessary, filters be installed in treatment plants before the water is disinfected.

'We also need to ensure that suppliers' water safety plans include a requirement that causes of contamination are investigated and then steps are taken to address those causes.”

Water New Zealand Chief Executive John Pfahlert hopes the investigation into the Havelock North contamination will provide a real opportunity to investigate the significant challenges many local authorities face in ensuring communities have safe drinking water and that any contamination outbreaks are investigated and dealt with appropriately.