Measuring the salinity or dissolved salt content of water is important as aquatic organisms, livestock and crops thrive at different salinity levels.  Freshwater has a salinity value of less than 0.5 ppt while seawater has an average salinity of around 35 ppt.  

 LAQUAtwin Salt EC

Salinity is the measure of the amount of dissolved salts in water.  It is usually expressed in parts per thousand (ppt) or percentage (%).  Within an estuary, the salinity levels are referred to as oligohaline (0.5 - 5.0 ppt), mesohaline (5.0 - 18.0 ppt) or polyhaline (18.0 - 30.0 ppt).  Near the connection with the open sea, estuarine waters may be euhaline, where salinity levels are the same as the ocean at more than 30.0 ppt.  

Salinity varies from place to place in the ocean, but relative proportions of most major dissolved constituents remain virually constant.  

Salinity is often derived from Electrical Conductivity (EC) measurements.  EC is measured by passing an electric current between two metal plates or electrodes in the water sample, measuring how readily the current flows between the plates.  The use of EC measurements to estimate the ionic content of seawater led to the development of the Practical Salinity Scale 1978 (PSS-78).

The PSS-78 has been considered by the Joint Panel on Oceanographic Tables and Standards and iis recommended by all oceanographic organisations as the scale in which to report future salinity data.  

The LAQUAtwin Salt 11 Pocket Meter measures the conductivity value of a sample then converts it to a salinity value based on the salinity standard curve selected.  The sensor has two titanium metals coated with platinum black that resist corrosion and a temperature sensor for accurate measurements.  The meter is programmed with two standard calibration curves - sea water and sodium chloride (NaCl).


Calibrate the LAQUAtwin Salt 11 Pocket Meter according to the instructions provided with the instrument, using the 0.5% (5 ppt) and 5.0% (50 ppt) NaCl Standard Solutions included in the kit. 

Prior to calibration, make sure to select the standard calibration curve (either NaCl or Seawater) and the unit (either % or ppt) depending on your application and reporting unit requirements.  If both the sea water curve and ppt unit is selected, calibrate the meter with the 5 ppt NaCl standard.  It is best to use 5 ppt and 50 ppt seawater standards if available. 

Sample Collection and Measurement

Place drops of water onto the sensor using the pipette which is included in the kit. Make sure the sample sell is completely filled-up with sample and that there are no bubbles formed.  Record the salinity reading once it is stable. 

Before testing another sample, rinse the sensor with DI (Distilled or Deionised) Water or with the next sample to be tested, and dab a soft tissue to remove the remaining water trapped inside the sample well. 

Results and Benefits

Salinity is an important measurment in seawater or in estuaries where freshwater from rivers or streams mixes with salty ocean water as aquatic organisms have varying abilities to survive and thrive at different salinity levels.  Saltwater organisms survive in salinity levels up to 40 ppt, yet many freshwater organisms cannot live in waters with salinity levels above 1 ppt. 

Salinity affects the dissolved oxygen (DO) levels in water.  The solubility of oxygen in water decreases as salinity increases.  The solubility of oxygen in seawater is about 20% less than it is in freshwater at the same temperature. 

For a copy of the full Application Note - Measuring Salinity of Water, please contact us