As the water passes through the sanitizer, all micro-organisms are killed,  leaving the cleanest and purest water possible for return back into your pool. For residential pools this effectiveness allows you to lower the amount of chemicals that you will use in your pool by 50% or more, unfortunately it is not possible to build a pool where 100% of the water passes through a filter so a small residual of chemical should remain to combat any organisms on the pool walls and hardware. If you or your children are sensitive to chlorine then this could be the perfect solution for your backyard pool enjoyment.  Minimum bugs using minimal chemicals!!