TDS - Total Dissolved solids
TDS means dissolved ion like Calcium (Ca),Magnesium (Mg),Sodium (Na),Chloride (Cl),etc.Which is dissolved in water.
It is measured in parts per million.
As per conductivity analysis of water we can predict TDS by formula given below
TDS = Conductivity * Factor
Factor = Generally it is between 0.50 to 0.70
It is different as per type of water.You can know exact factor by gravimetric analysis method of TDS.Most of the cases 0.67 is used.
What is salinity?
Salinity means salt content which is dissolved in water.It is measured in parts per thousand.
Sea water salinity is around 40 ppt means 1 kg of of sea water contains 40 grams of salt.