Here is what the BRITA site says:
1. MEMO BRITA behaves like an alarm clock that would sound after 4 weeks to invite to replace the cartridge regardless of its actual wear (it effectively ensures turnover BRITA).
2. The actual length of the cartridge depends on the characteristics of your water and the number of liters you treat him.
3. The disposal part of the limestone by ion exchange salts (as in a dishwasher) depends mainly on the hardness of your water (dissolved calcium content), which varies greatly from one place to another, in a report January to March or even more.
When she absorbed all the limestone which it is capable, it does not absorb anything.
4. The activated carbon part captures odors (chlorine, etc.) and some heavy metals that attach to the surface.
When she absorbed everything she can, she does not absorb anything.
5. My first conclusion is that BRITA took a good margin of safety by replacing the cartridge every 4 weeks.
It may be that the cartridge is really saturated in the existing worst place in France, but certainly not at home.
6. My second conclusion is that actually spent cartridge lets it retains more.
It is like taking water directly from the tap, which is not fatal.
