What does softened water mean in practice?
After sodium exchange, it is low in calcium and magnesium, but contains more sodium and a similar total number of ionic equivalents.
When does it matter?
It is not demineralized water and still conducts electricity, it contains chlorides, sulfates and other components of raw water.
Which solutions are related to it?
Residual hardness and sodium are controlled in sensitive applications, and a downstream RO process is used to remove salts.