Subject: Why does the brita water filter need to be replaced?

I ask this question because I am doing research on the brita filter and I 
found it hard to find information I needed. Brita.com was not very helpful 
and I was hoping that this might be. I would just like to know more about 
the chemistry of it. I know it works with an ion exchange resin and 
activated carbon, but I am still unsure how they work and why it loses its 
filtering abilities after a month. Thanks for your help

Re: Why does the brita water filter need to be replaced?