A study looking at whether water supplies are meeting drinking water standards has highlighted ongoing problems experienced by some suppliers.
The study’s results, which are being presented in a paper to the September conference of Water New Zealand' by ESR research scientist David Wood, examines seven years of data collected on the achievement of the drinking water standards.
Since 2008, it has been a legal requirement for water suppliers to to take all practicable steps to comply with the water standards, and for the Director-General of Health to publish an annual report on drinking water quality.
The research paper reviewed data from annual surveys of networked drinking supplies serving more than 100 people that have failed to meet drinking water standards, to determine the causes of the transgressions and identify the risk factors associated with transgressions.
The presence of E.coli in drinking water is an indication that it has been faecally contaminated and has the potential to contain pathogens, which poses a risk for anyone drinking the water. Too many E. coli transgressions are a major reason for water suppliers failing to meet the standards.
David Wood says that E. coli has been identified at least once in approximately 40 per cent of supplies over seven years of the survey.
A 2015 study looking at why drinking water supplies were failing to meet E.coli standards concluded that treating water with chlorine would help water suppliers meet the standards required. It also said that finding the cause of the transgression was an important part of preventing any further postive tests for E. coli.
However this study, which includes research conducted through interviews with local drinking water assessors, has found that although chlorination is a protective factor, disinfection systems can fail.
The research also found that supplies that relied on water from secure groundwater sources tended to have a higher rate of transgressions because these supplies do not generally have disinfection, which reduces protection from contamination once water has been drawn from the ground.
He says that overall, larger suppliers have lower failure rates than smaller suppliers.