Abstract: The present invention relates to a method of reducing the concentration of contaminant ions, preferably nitrates ions, in impure water. The method comprises steps of: a) passing the impure water through an ion exchange resin to substitute regenerant ions from the resin for dissolved contaminant ions; b) passing a relatively dilute aqueous solution of wash-out ions through said resin to substitute wash-out ions for contaminant ions bound to the resin and; c) passing a relatively concentrated aqueous solution of regenerant ions through said resin to substitute regenerant ions for wash-out ions bound to the resin. The affinity of the resin to wash-out ions diminishes from being greater than that for contaminant and regenerant ions when exposed to a relatively dilute ionic solution to being less than that for said contaminant and regenerant ions when exposed to a relatively concentrated ionic solution.