volume the relative proportions of the three resins has been found through testing and calculation to achieve the desired results with the microporous and macroporous anion resins of approximately equal thickness beds in the container the cation resin is twice the combined thickness or 67 two thirds of the total resin volume in order to approximate the purifying lifetime of the anion resins thus each anion resin bed is one sixth of the total resin volume since one of the objectives of the present invention is to provide a lifetime between resin recharges that ends at a time when the three resins are each approaching the need for the passage of a brine or other recharge solution therethrough the amount of cation required has been found to be approximately twice the volume of the anion resins an activated charcoal bed 26 is shown at the top of the mixed media charge since the charcoal is normally the lightest component of the mixture this is the case when using low cost carbonized coconut shells however heavier carbons may well form a lower layer in the strata the carbon has been found to regenerate through the back flush with brine either sodium or potassium typically the weight per unit volume of charcoal formed of carbonized coconut shells is 22 lbs per cubic foot so that it readily separates to form the top layer the carbon utilized for the removal of bacteria and for flavor enhancement of the water may be omitted in.