4e3eafac_ell_Water_Treatment_Strategies__What_it_does
[Treatment process] Ion exchange (softening, etc) See how a water softener works [Contaminants Removed/Altered] Hardness (calcium, magnesium), iron, manganese are commonly removed. Other ions such as arsenic, radium and nitrates can be removed this way. [What it does] 
As water runs through a resin in a vessel, charged electrical particles (ions) are exchanged for other ions which are more desirable. Often the resin can be regenerated automatically for years of service. In industrial settings, a very similar process is used to make ultra high purity water. Most residential and commercial applications are oriented toward nuisance mineral control though we have had some success reducing arsenic and radium with this method.
Well Water Treatment Strategies
What it does