When the resin becomes saturated with calcium and magnesium, it must be recharged. The recharging is done
by passing a salt (brine) solution through the resin. The sodium replaces the calcium and magnesium which are discharged in
the waste water.
Hard water treated with an ion exchange water softener has sodium added. According to the Water Quality
Association (WQA), the ion exchange softening process adds sodium at the rate of about 8 mg/liter for each grain of hardness
removed per gallon of water.
For example, if the water has a hardness of 10 grains per gallon, it will contain about 80 mg/liter of sodium
after being softened in an ion exchange water softener if all hardness minerals are removed.
Because of the sodium content of softened water, some individuals may be advised by their physician, not
to install water softeners, to soften only hot water or to bypass the water softener with a cold water line to provide unsoftened
water for drinking and cooking; usually to a separate faucet at the kitchen sink.
Mechanically softened water is not recommended for watering plants, lawns, and gardens due to its sodium
content.