Several dissolved metals and heavy metals are monitored, all of which can affect the quality of groundwater for drinking-water supply. These metals may be derived from soil, rocks and minerals in the aquifer as water passes through them, as well as from anthropogenic sources including agricultural and industrial activities. Concentrations of many dissolved metals, for example iron and manganese, are controlled by the redox state of the water — when the concentration of dissolved oxygen in the water is low (often in older, more evolved groundwater) these metals tend to be more soluble. Switch tabs below to look at different dissolved metals.
Map usage: Drag and scroll on the map to move and zoom in on areas of interest, click on a site circle to see more information and subset the table below to that specific site, and use the selection box on the map ( ) to subset table data to sites in that area.
Table usage: All data are dissolved metal concentrations (mg/L). Click on the +/- button at the end of a row to see the raw sample data and highlight that site on the map above. Click on table headers to sort the data by that column – holding the shift key allows sorting over multiple columns.
| Concentration rating | No. Sites |
|---|---|
| Below detection limit (<0.02) | 34 |
| Low (0.02 to 0.3 mg/L) | 10 |
| Exceeds aesthetic value (>0.3 mg/L) | 18 |
| Total sites | 62 |
Groundwater dissolved iron concentrations are evaluated below in terms of the drinking water aesthetic value of 0.3 mg/L (Taumata Arowai, 2022). Concentrations above this may cause staining of laundry and sanitary ware.
Sites with annual median concentrations above the aesthetic threshold value are flagged as ‘Exceeds aesthetic value’.
| Concentration rating | No. Sites |
|---|---|
| Below staining threshold <0.04 mg/L) | 39 |
| Below taste threshold (0.04 to 0.1 mg/L) | 4 |
| Above taste threshold (0.1 to 0.4 mg/L) | 7 |
| Exceeds DWSNZ (>0.4 mg/L) | 12 |
| Total sites | 62 |
Groundwater dissolved manganese concentrations are evaluated below in terms of the Drinking Water Standards for New Zealand (DWSNZ), as excess concentrations can have negative health effects. Manganese concentrations are also assessed against aesthetic values of 0.04 for staining and 0.1 mg/L for taste (Taumata Arowai, 2022).
Sites with annual median concentrations above the DWSNZ Maximum Acceptable Value (MAV) of 0.4 mg/L are flagged as ‘Exceeds DWSNZ’.
| Concentration rating | No. Sites |
|---|---|
| Below detection limit (<0.001) | 47 |
| Low (0.001 to 0.01 mg/L) | 12 |
| Exceeds DWSNZ (>0.01 mg/L) | 3 |
| Total sites | 62 |
Groundwater dissolved arsenic concentrations are evaluated below in terms of the Drinking Water Standards for New Zealand (DWSNZ), as excess concentrations can have negative health effects.
Sites with annual median concentrations above the DWSNZ Maximum Acceptable Value (MAV) of 0.01 mg/L are flagged as ‘Exceeds DWSNZ’.
| Concentration rating | No. Sites |
|---|---|
| Below detection limit (<0.0005) | 59 |
| Low (0.0005 to 0.05 mg/L) | 3 |
| Exceeds DWSNZ (>0.05 mg/L) | 0 |
| Total sites | 62 |
Groundwater dissolved chromium concentrations are evaluated below in terms of the Drinking Water Standards for New Zealand (DWSNZ), as excess concentrations can have negative health effects.
Sites with annual median concentrations above the DWSNZ Maximum Acceptable Value (MAV) of 0.05 mg/L are flagged as ‘Exceeds DWSNZ’.
| Concentration rating | No. Sites |
|---|---|
| Below detection limit (<0.0001) | 50 |
| Low (0.0001 to 0.01 mg/L) | 12 |
| Exceeds DWSNZ (>0.01 mg/L) | 0 |
| Total sites | 62 |
Groundwater dissolved lead concentrations are evaluated below in terms of the Drinking Water Standards for New Zealand (DWSNZ), as excess concentrations can have negative health effects.
Sites with annual median concentrations above the DWSNZ Maximum Acceptable Value (MAV) of 0.01 mg/L are flagged as ‘Exceeds DWSNZ’.
| Concentration rating | No. Sites |
|---|---|
| Below detection limit (<0.001) | 4 |
| Low (0.001 to 1.5 mg/L) | 58 |
| Exceeds aesthetic value (>1.5 mg/L) | 0 |
| Total sites | 62 |
Groundwater dissolved zinc concentrations are evaluated below in terms of the drinking water aesthetic value of 1.5 mg/L (Taumata Arowai, 2022). Concentrations above this may have noticeable taste.
Sites with annual median concentrations above the aesthetic threshold value are flagged as ‘Exceeds aesthetic value’.