Groundwater Salinity
Salinity, a measure of the total amount of salts dissolved in groundwater, is a good indicator of its suitability for various uses. The map shows generalised zones of groundwater salinity.
Note that on a local scale salinity can vary considerably. The map is highly generalised. The actual limits that the colours are based on are:
| Very Fresh | Less than 500 mg/litre | Suitable for most uses |
| Fresh | 500 to 1500 mg/litre | Suitable for most uses |
| Brackish | 1500 to 3000 mg/litre | Unsuitable for human consumption but suitable for only limited irrigation |
| Saline | More than 3000 mg/litre | Suitable for limited stock and industrial uses |
Where Do The Salts Come From?
Salts in groundwater originate either from minute quantities dissolved in rain water, from the chemical breakdown of rocks or from direct connection to sea water.
Saline waters are found mainly in the southern part of the Northern Territory due to a combination of low rainfall and high evaporation. In the northern areas groundwaters are mainly fresh because the high rainfall tends to flush away salt before it has a chance to be concentrated by evaporation.
Saline waters found along the coastline occur beneath low lying coastal plains. Aquifers beneath the plains are either recharged by tidal rivers or contain "fossil seawater that remained in the sediment since it was laid down in an estuarine environment, thousands of years ago.
Salts and Town Supplies
The groundwater with the best quality available is naturally utilised for town supplies. The graph below shows the total salt content (salinity) and chloride contained in the groundwater supplies of the four main towns in the Northern Territory.
