On Jun 5, 2:12*pm, Herodotus wrote:

Further, I have had an activated charcoal filter for drinkable water
using the cartridge disposable household plumbing in-line filter for
years but have no idea as to how often one should change them.

Activated charcoal filters remove chemicals, including chlorine, by
adsorbing them onto sites on the surface of the charcoal. The number
of such sites on any one filter is limited, so the filter has a
limited life.

When using an AC filter to rid drinking water of chemicals causing
offensive tastes and smells, you'll know (by taste and smell) when to
change the filter.

For removing chlorine from town water such that the filtered water can
then be used to flush RO membranes, the story is more complicated.

Other than testing the level of free chlorine in the filtered water
(pool stores sell test kits for chlorine), I know of no way of testing
the effectiveness of an AC filter at removing chlorine. And I don't
know if an AC filter, stored dry, loses any of its adsorbed chlorine
(I suspect it must, but how much and how long it might take is unknown
to me).

The usual advice is to change the filter (some filters come with
advice about changing them every 3K litres/1K gallons, or every 6
months). AC filters are less expensive than RO membranes, so you
should err on the side of caution and just change the filter.

Cheers

Bil