The WK1P is intended for use on plastic pipe up to 2 1/2" diameter on re-circulating systems for swimming pools. It may also be used to treat domestic water supplies on pipe diameter up to 1" where it is exposed to wet or damp conditions. It MUST NOT be used on pipe sizes of more than one inch diameter except on re-circulating systems such as pools. The WK1P is fully waterproof so it can be left outside exposed to rain and weather.