Does a Britta water filtering pitcher need toiveling?
Wikipedia explains how the Britta pitchers are made:
BRITA products include water jugs, kettles and tap attachments, all of which use silver-impregnated activated carbon and ion-exchange resin disposable filters as their primary filtering mechanism. The activated carbon used in BRITA filters is produced from coconut shells. The company manufactures its pitchers from styrene methyl methacrylate copolymer.
Coconut shells would not require tevilla.
As for the pitcher itself which is, essentially, plastic, Kof-K says:
The consensus of the majority of the poskim is that utensils made from plastic do not require a tevilah prior to use. An example of this is Tupperware utensils. There are some poskim who say that fortunate is the one who is careful to tovel plastic. The same holds true for utensils made from rubber.
Refer to the footnotes in each article for additional info and details.