Assessment of chemical quality of drinking water in regional New South Wales, Australia

As drinking water quality is directly related to health, it is important for water utilities to monitor and assess the quality of their drinking water supply. New South Wales Health has maintained a comprehensive drinking water monitoring program for non-metropolitan areas of the state since 2001. Over 214,000 chemical and physical test results from 322 public drinking water supply systems were recorded in the monitoring database from 2001 to 2007. The study presents the analysis of the chemical characteristics of drinking water from this most complete regional drinking water database in Australia. We assessed the chemical quality of drinking water and examined the association between the compliance of chemical characteristics and explanatory factors. We defined a supply system as non-compliant if the 95^thpercentile of any health-related characteristic was greater than the guideline value from the Australian Drinking Water Guidelines 2004 over the seven year assessing period. The explanatory factors included the supply system population, treatment, water source and other related characteristics. Generalized linear models were applied with the appropriate model goodness-of-fit test and diagnostics. Over seven years, 80% of supply systems were compliant with guideline values for all health related characteristics. The most frequent non-compliant characteristics were lead, antimony, nickel and manganese. A number of these non-compliant characteristics could arise from the materials used in pluming. Further investigation is needed to confirm the source of some non-compliant characteristics. We concluded that compliance of supply systems was significantly correlated with population (odds ratio 0.82 for each 1000 increase with 95% CI: 0.69-0.97), and inversely correlated with median total hardness (odds ratio 1.06 for 20 mg/L increase with 95% CI: 1.01-1.11). The marginal effect of a change with the interaction between treatment and turbidity, and other important factors affecting compliance were also considered. The results from this study provide a better understanding of the factors associated with chemical compliance of drinking water, including the benefit of particle removal (and turbidity reduction) in improving the chemical quality of drinking water. In particular, the findings of this study should prompt managers of water utilities to examine carefully the water quality data available to them. Water utilities should review their data on source water and drinking water to determine whether there is a need to optimise or add treatment processes.