Chemical analysis - Gear Island
The following table shows the mean values of chemical analysis of the water supply from the Gear Island Water Treatment Plant, for the year ended 30 June 2011, 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: Values that are preceded by the '<' symbol indicate the detection limit for that test. (A) Drinking-water Standards for New Zealand 2005 (Revised 2008); MAV denotes 'Maximum acceptable values for inorganic deterrminands of health significance'; GV denotes 'Guideline values for aesthetic determinands'. A dash in the 'GV or MAV' column indicates that there is no applicable value. (B) See Hardness. (C) The fluroide content recommended for drinking water by the Ministry of Health for oral health is 0.7 to 1.0 mg/L. (D) Annual mean values for copper typically <0.1 - we found an issue with the sampling point, which has been corrected. (E) We no longer require our laboratory to test for treated water alkalinity. We are now testing for raw water alkalinity and using that to adjust pH to achieve a suitable Langelier saturation index.
|
Test |
DWSNZ MAV/GV |
No. of samples |
Value |
|
Alkalinity (total), mg/L CaCO3 |
- |
1 |
58 |
|
Aluminium (acid soluble), mg/L |
0.10 |
2 |
<0.002 |
|
Arsenic (total), mg/L |
0.01 |
1 |
<0.002 |
|
Boron, mg/L |
1.4 |
1 |
<0.05 |
|
Cadmium (total), mg/L |
0.004 |
1 |
<0.001 |
|
Calcium (total), mg/L |
(B) |
- |
- |
|
Chloride, mg/L |
250 |
1 |
15.3 |
|
Chromium (total), mg/L |
0.05 |
1 |
<0.001 |
|
Conductivity, mS/cm @ 25 oC |
- |
1 |
17.2 |
|
Copper (total), mg/L |
2 |
12 |
<0.013 |
|
Cyanide (total), mg/L |
0.6 |
1 |
<0.005 |
|
Fluoride, mg/L |
1.5 (C) |
52 |
0.83 |
|
Hardness (total), mg/L CaCO3 |
200 |
3 |
24.0 |
|
Iron (total), mg/L |
0.2 |
13 |
0.061 |
|
Lead (total), mg/L |
0.01 |
1 |
<0.001 |
| Magnesium (total), mg/L | (B) | - | - |
|
Manganese (total), mg/L |
0.4 |
12 |
<0.013 |
|
Mercury (total), mg/L |
0.007 |
1 |
<0.001 |
|
Nickel (total), mg/L |
0.08 |
1 |
<0.001 |
|
Nitrate, mg/L -N |
50 |
1 |
1.05 |
|
pH |
7.0-8.5 |
13 |
7.50 |
|
Selenium (total), mg/L |
0.01 |
1 |
<0.005 |
|
Silica (molybdate-reactive), mg/L |
- |
1 |
16.7 |
|
Sodium (total), mg/L |
200 |
1 |
25.4 |
|
Solids (total dissolved), mg/L |
1000 |
1 |
115 |
|
Sulphate, mg/L |
250 |
1 |
6.07 |
|
Zinc (total), mg/L |
1.5 |
12 |
<0.013 |