The following table shows the mean values of chemical analysis of the water supply from the Wainuiomata Water Treatment Plant, from 1 July 2019 - 30 June 2020, compared with the maximum allowable value (MAV) or guideline value (GV) for each element as set out in the Drinking Water Standards New Zealand (DWSNZ).
Notes: (A) MAV denotes the maximum acceptable value to comply with the Drinking-water Standards. (B) GV denotes the maximum guideline value in the Drinking Water Standards.
Parameter DWSNZ MAV (A) / GV (B) No of samples Mean value Max value Alkalinity - total g CaCO3/m³ - 13 31.23 38 Aluminium - total g/m³ 0.1 (B) 14 0.0325 0.052 Arsenic - total g/m³ 0.01 (A) 2 <0.002 <0.002 Boron - total g/m³ 1.4 (A) 2 <0.05 <0.05 Cadmium - total g/m³ 0.004 (A) 2 <0.001 <0.001 Calcium hardness g CaCO3/m³ 200 (B) 13 29.23 36 Chloride g/m³ 250 (B) 1 23.1 23.1 Chromium total g/m³ 0.05 (A) 2 <0.001 <0.001 Conductivity at 25°C mS/m - 1 15.3 15.3 Copper - total g/m³ 2 (A) 13 <0.013 <0.013 Cyanide g/m³ 0.6 (A) 2 <0.005 <0.005 Fluoride g/m³ 1.5 (A) 107 0.07 0.45 Hydrogen sulphide g/m³ 0.05 (B) 1 <0.05 <0.05 Iron - total g/m³ 0.2 (B) 13 0.034 0.065 Lead - total g/m³ 0.01 (A) 2 <0.001 <0.001 Manganese - total g/m³ 0.04 (A) 13 0.048 0.048 Mercury - total g/m³ 0.007 (A) 2 <0.001 <0.001 Nickel - total g/m³ 0.08 (A) 2 <0.001 <0.001 Nitrate - nitrogen g/m³ 50 (A) 2 0.035 0.04 pH 7.0-8.5 (B) 14 7.807 8.3 Selenium - total g/m³ 0.01 (A) 2 <0.005 <0.005 Silica g/m³ - 2 12.6 13.7 Sulphate g/m³ 250 (B) 1 4.43 4.43 Total dissolved solids g/m³ 1000 (B) 1 75 75 Zinc - total g/m³ 1.5 (B) 13 0.016 0.016