How do we know when to change the cartridges?

We recommend that you trust your senses of smell and taste. There is warning of imminent depletion because the flow of water slows out of the tap. Final depletion is marked and sudden and most of our customers carry a spare cartridge against this eventuality.

Alternatively, we can supply an automatic shut-off water meter. You can set this for the amount of water we give for each model and the meter will shut off the filtered water at the specified amount.

There is more information at 'cartridge life explained'.

There are systems available (not from us) with an indicator. It is easy to assume that these indicators are measuring contaminants - they do not. In fact, they are measuring a pressure drop caused by particles on the surface of the cartridge. This is NOT a measure of cartridge depletion as the activated carbon for chlorine and chemicals may still be active - or if the water is clean, it may not measure at all so showing, inaccrately, that the cartridge is not depleted.