[dharma1]

Those filters (usually coconut shell carbon) can start having bacterial biofilm grow on them over time, and generally get saturated with gunk, that’s why you’re meant to change them frequently. I guess when they do depends on a lot of factors and the recommendation is an average length - ideally would have some better sensors on when to change them but gets more costly

[lazide]

And (defensibly, somewhat) they’ll of course set the indicator to be for the worst case possible, even if not probable, so they 1) get more money, and 2) won’t lose money in lawsuits from someone saying ‘It still said it was fine!’ who gets sick, even if there were other really obvious signs something was wrong.

So for a filter, either 24/7 use or one time use then letting it sit (whichever is worse).

[alistairSH]

And yet water filters for use when camping last WAY longer and don't cost that much more. A simple Katydid BeFree lasts 1000L. I'm betting the Brita indicator came on WAY before that.