Pump coloured water through the canister as shown.

If the purified water is still coloured - even faintly - the internal canister matrix has most likely been damaged and the canister cannot be relied upon under this condition and must be replaced.*

* Note: Because the initial flow from a new purification canister may contain black "fines" from the manufacturing process, it is best to pump at least a litre of water before doing an integrity test to avoid posible confusion.