Water treatment system and method

Abstract

A method and apparatus for producing purified water. Treated water may be provided for domestic use wherein the water may be treated by removing selected dissolved species while retaining properties that may improve the properties or aesthetics of the water.

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         11 . A method of selectively retaining ions in a water supply comprising:
 passing a feed water through a depleting compartment of an electrochemical device, the feed water comprising monovalent and divalent ions;   removing at least 30% of the divalent ions from the feed water and retaining at least about 80% of a species selected from silica, boron and fluoride, to produce a treated water; and   supplying the treated water for household consumption.   
     
     
         12 . A method of producing a purified water comprising:
 passing a water stream through a depleting compartment of an electrochemical device; and   adjusting a voltage applied to the electrochemical device to control the current passing through the electrochemical device at a level adequate to remove greater than about 25% of any hardness ions in the water stream and inadequate to remove greater than about 10% of any fluoride or silica species from the water stream.   
     
     
         13 . The method of  claim 12  wherein less than 10% of any fluoride species is removed. 
     
     
         14 . The method of  claim 12  wherein less than 10% of any silica species is removed. 
     
     
         15 . The method of  claim 12  further comprising passing the purified water through the depleting compartment a second time. 
     
     
         16 . The method of  claim 12  wherein the electrochemical device comprises an electrodeionization device. 
     
     
         17 . The method of  claim 12  wherein the electrochemical device comprises an electrodialysis device. 
     
     
         18 . A method comprising:
 passing a feed water through a bed of ion exchange material to remove greater than 30% of any hardness ions from the feed water to produce a softened water;   supplying the softened water for household consumption; and   discharging a concentrated solution comprising calcium, wherein the sum of the ionic content of the softened water and the ionic content of the concentrated solution is no greater than the total ionic content supplied by the feed water.   
     
     
         19 . The method of  claim 18  wherein the softened water is less corrosive than the feed water. 
     
     
         20 . The method of  claim 18  further comprising applying an electric current across the bed of ion exchange material.