Water softeners work by passing water through a bed of ion exchange resin beads which are naturally charged with sodium ions. When hard water passes
through these resin beads it is softened by exchanging hardness ions with sodium ions & this is known as an ion exchange process. Eventually the resin
beads will be depleted of sodium ions & at this point they will need to be regenerated. This is done in a fully
automated process known as a regeneration
cycle using food grade salt.
Salt is made up of two ions, a positively charged sodium ion (na) & a negatively charged chloride ion (cl). During a regeneration cycle, salt is introduced into the system & the ion exchange resin beads naturally regenerate themselves by attracting sodium ions from the salt. The remaining chloride ions are then sent to drain along with captured hardness ions during the regen process & never enter your water supply.
Softened water is not corrosive & the removal of hardness with a water softener does not cause or even
accelerate corrosion. The Corrosiveness of water
is caused by a number of other factors which are
unrelated to the water softening process. The misconception that water softeners cause corrosion because
they use salt is often promoted by competitors selling inferior products who don't fully understand the
chemistry behind the process. Only the sodium
ion (na) from salt enters your water supply in exchange for hardness ions while the corrosive chloride ion (cl) is sent to drain in a fully automated process.
Below is an extract taken directly from the WQA website stating the facts.
"The suggestion that ion exchange water softeners promote corrosion is a misperception and the suggestion to use scale build up as a corrosion control method is inappropriate as proven by the EPA. The conclusions were drawn from an EPA pilot study conducted by Thomas J. Sorg and Michael R. Schock of the EPA's Drinking Water Research Division as project manager and principal investigator. Simply put, the removal of hardness with an ion exchange water softener does not affect the factors which cause or even accelerate corrosion. Corrosion is caused by a change in the pH or carbon dioxide concentration, the dissolved oxygen concentration, or the total chemical concentration of minerals. None of these factors is affected by water softeners."
The amount of sodium in softened water will depend on how hard the water was before it was treated. Sodium content will increase by roughly 7.92mg/L for
every 17.14 ppm increase in hardness.
A standard glass of softened water with 250ppm hardness reduction will contain approx. 28.9mg of sodium. In contrast, a tablespoon of skimmed milk contains around 120mg of sodium & a slice of white bread contains around 170mg of sodium.
The HSE's RDA of sodium intake is 2500mg per day for men & 2000mg per day for women. The HSE's definition for "Low Sodium" in foodstuff is anything with less than 40mg of sodium per 100ml. This puts softened water into the "Low Sodium" bracket meaning that its consumption will make little contribution to your average daily sodium intake.