Paul,

This phenomenon confuses lots of people...

Remember, your softener is softening the water by ion exchange and if you're using NaCl as a regenerant the exchange is at 2 sodium ions for each ion of hardness.

The harder the water being softened the more sodium is exchanged (@ 2 for 1).

See where we're going? Remove 100 ions of hardness and the softener adds 200 ions of sodium. That's how your TDS increases when softening water.

The lower the hardness of the service water the less noticeable the increase in TDS will be. The harder the service water the greater the increase in TDS will be but only someone who buys a tester and goes looking for confusion will ever see it.

If your softener is correct sized for the # of people, the water conditions, SFR, and it is set up to regenerate efficiently and the water feels soft then all is well.

Your TDS tester is the right tool to monitor the RO. Routine replacement of the pre and post filters is important, but when the TDS tester shows that the rejection rate falls below 90% it's time for a new membrane

Thanks for the response Justa...

Confusing is the right word.

I thought that the Ca and Mg ions in the incoming city water supply met the zeolite inside the water softener and attached to the zeolite itself.

Doesn't the briny regeneration simply reverse the attachment of Ca and Mg ions to the zeolite and flush the loosened Ca and Mg ions, now in the brine wash, to the city wastewater system as part of the brine waste ?

My understanding, limited as it is, was that the sodium or potassium chloride wash and rinse cycle cleansed the zeolite and only a small amount of that brine process would seep into the house system.

If most of what I am measuring downstream from the water softener is sodium or potassium, rather than Ca or Mg solids in the water, we are presented with quite a dietary dilemma. A liter of water from the tap would contribute around 445 milligrams of sodium to one's daily intake towards an RDA of 1,300 mg per day. Guess I'd better drink the R/O water at a TDS of 28 ppm, or 28 mg/L, after all.

Paul

If you want to learn the chemistry of ion exchange there are volumes you can read and years you can invest. Water softening is ion exchange... not ion wash or ion rinse.

Regarding the increased sodium in the softened water... we are talking ions exchanged not grams and your TDS meter is measuring PPM. Sodium exchanged into soft water is roughly 7.85 mg/l per grain of hardness exchanged. So 10 gpg * 7.85 = 78.5 mg/l. A slice of white bread has 150 mg of sodium. A glass of skim milk is 530

What you are measuring downstream of the softener is sodium or potassium along with whatever else is in the water when it enters your home that is not ion exchanged out by the softener.

Most people with hardness at your level and above do drink and cook and make ice cubes with RO water.