Is softened water more corrosive than untreated tap water?
Generally, No! Naturally soft waters of low alkalinity and those from an ion-exchange softener can have increased potential for corrosion. pH of these waters has tendency to become more alkaline when heated in open vessel – water of pH more alkaline than 8.4 is corrosive towards aluminium. Softening water does not significantly increase pH. The Water Supply (Water Quality) Regulations 2000 allow mains water to be up to pH 10 in England and Wales (pH 9.5 in Scotland). Recent testing has shown that softening water may actually make it less corrosive towards typical heating system metals, such as iron and copper, as it removes heavy metal contaminants which can accelerate corrosion.
