NSA Water Purifier Bacteriostatic Water Treatment System Water Filter. The active purpose of this unit is to remove chlorine taste, colour and odour. This is done by the use of active carbon. from drinking water. The unit is designed to accomplish this purpose through the use of a special silver impregnated carbon media bed. The unit is designed to ensure that there is no silver emission into the water in excess of EPA standards for safe drinking and is registered with EPA on that bases. $40. without carafe carafe incl.