Each year ESR surveys all networked water suppliers that provide water to more than 100 people for information on their achievement of the Drinking-water Standards for New Zealand (the Standards). This information is used to prepare the Annual Report on Drinking-water Quality for the Ministry of Health. The study reported here analysed four years of survey data 2010-2014 (341 zones). The study focused on zones that did not achieve the Standards for E. coli or chemicals. Its aim was to better understand the reasons for non-achievement to help improve risk management.
The study found the main reason for zones failing to meet the E. coli and chemical requirements of the Standards was too many transgressions (maximum acceptable value exceedences). Almost all zones with an excessive number of transgressions, for both E. coli and chemicals, served populations in the 501-5000 bracket. Corrective actions were considered adequate in 91% of zones with E. coli transgressions, despite repeated failures over the four years. In contrast, in 23% of zones with chemical transgressions, corrective actions were considered adequate.
Actions are being taken to address both bacteriological and chemical non-achievement in some zones. This should results in improve levels of achievement when treatment upgrades take effect.