Water Softener 6/10: Why is TDS reading high after installing water softener?

For those who are curious on why TDS meter shows slightly higher reading after Installing a salt based softener, below explanation maybe helpful. This is one of the common question that gets asked by many homeowners in our circles and those we have had the privilege of helping. Total Dissolved Solids (TDS) meter measures / reads what is called as electrical conductivity. In other words it is a measurement more related to charged ions or charged particles in water.


Water typically contains both charged and non charged particles. Examples of non charged particles include non-polar (bit of a chemistry terminology) molecules such is oxygen, nitrogen etc. Examples of charged particles include sodium, calcium etc. Now let's try to understand TDS a bit in detail. Generally speaking the higher the hardness of water, the higher the TDS reading. 1 grain ~ 17.1 PPM i.e 17.1 milligrams per gallon.


So, if the TDS reading shows 3 i.e., 51.3 PPM ( 51.3 milligrams per gallon) , there is no way for us to know if those 51.3 milligrams are due to calcium or sodium or potassium etc. This is due to the fact that TDS meter only measures charged particles and calcium, sodium & potassium all being charged particles and ignores measuring the presence of non-polar molecules. As we all / many of us know, water hardness is primarily defined by the amount of calcium (mainly) & magnesium present in water.


That said, during the softener ionization process, two sodium ions replace a singe ion to get rid of calcium (removal of hardness). Hence, after adding the salt based softener, it is typical that people experience higher TDS reading. It does not mean, the softener or other systems downstream are not working. It only means, more charged particles are present now vs before. More dependable way to check if softener is working or not, is by using specialized hardness testing kits as opposed to TDS meter. The good uses for TDS meter are 1. To know if your Reverse osmosis system is working properly and if it is time to change filters 2. To get a general idea on whether a water filtration system or softener is needed.