Salinity - Dissolved Salts, Measuring Salinity
When we measure the salinity of water, we
look at how much dissolved salt is in the
water, or the concentration of salt in the water.
Concentration is the amount (by weight) of salt
in water and can be expressed in parts per
million (ppm). Here are the classes of water:



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Fresh water - less than 1,000 ppm
Slightly saline water - From 1,000 ppm
to 3,000 ppm
Moderately saline water - From 3,000
ppm to 10,000 ppm
Highly saline water - From 10,000 ppm
to 35,000 ppm
Ocean water has a salinity that is
approximately 35,000 ppm. That's the
same as saying ocean water is about
3.5% salt. Sometimes, salinity is
A student from the HIGH TIDE project
measured in different units. Another
turns on the CTD instrument. High school
common unit is the psu (practical salinity
students use the CTD recorder to
units). Ocean water has a salinity of
measure salinity, temperature and depth
approximately 35 psu. Scientists measure
of the water in the Lafayette River which
is a part of Chesapeake Bay.
Click on image for full size (54K JPEG)
Image courtesy of the HIGH TIDE project
salinity using a CTD instrument (CTD =
conductivity, temperature, depth).
Ocean water is about 3.5% salt. That
means that if the oceans dried up
completely, enough salt would be left behind to build a 180-mile-tall, one- milethick wall around the equator. About 90 percent of that salt would be sodium
chloride, or ordinary table salt. Chlorine, sodium and the other major dissolved
salts of the ocean are listed in this table:
Dissolved salts in
sea water (atoms):
55.3 % Chlorine
30.8 % Sodium
3.7 % Magnesium
2.6 % Sulfur
1.2 % Calcium
1.1 % Potassium
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