12. Measuring salinity
Most meters measure the electrical conductivity of water.
- Batteries are connected to two wires (electrodes). Salty water will conduct electricity between the two electrodes, the saltier the water, the more electricity is conducted.
- The unit of electrical measurement used is Siemens. The meter we use in the field measures milliSiemens (mS) per centimetre (the electrodes are one centimetre apart).
- Often the literature will use microSiemens (uS) and EC standing for electrical conductivity. These two units are the same. To convert milliSiemens to EC's or uS multiply the reading by 1000. The meter in the diagram shows 1.65 mS which is 1650 uS or EC's.
| Water Salinity Levels for Use | |||
| Source/Use | uS/cm or EC | Source | uS/cm or EC |
| distilled water | 0 | limit poultry | 5 800 |
| Murray R. (mouth) | 790 | limit beef cattle | 16 600 |
| desirable limit people | 830 | limit adult sheep | 23 000 |
| absolute limit people | 2 500 | Pacific Ocean | 58 000 |
Conversions
deciSiemens per meter (dS/m) = milliSiemens per cm (mS/cm) times by 1000 equals
microSiemens per cm (uS/cm) = Electrical Conductivity units (EC's)
Example 1.5 dS/m = 1.5 mS/cm = 1500 uS/cm = 1500 EC
Care of the meter
- Turn the meter off after use.
- Only place it in the water 2 cm.
- Don't put the electrodes in mud.
- If is accidentally dropped in the water please let your teacher know.
A salinity reading of 19.50 mS/cm is equal to:
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| management | investigation |