We have been using these water filters cartridges with our water jug BRITA Elemaris Meter XL Black Water Filter Jug for some time now.
We live on the Isle of Wight which is quite a hardwater area, and although I admit to being initially sceptical as to their use, thinking they were just another way to get me to part with money on a regular basis, I have been won over and can definitely see that they work!
The technical description is that the cartridges reduce limescale, chlorine and impurities.
In English they make the water taste better and really cut down on limescale forming in the kettle!
The recommendation is that the cartridge should be changed once a month; we get through about two full jugs of water a day, and have found they are actually effective for upto nearly two months.
The cartridges are very easy to install and are recyclable afterwards, most big supermarkets will take them (we drop off at a collection bin in our local Tesco's).
These cartridges will fit in all BRITA MAXTRA jugs, but do bear in mind you buy the right filters for the right jug (something we didn't initially do!).
The prices Amazon sell them for are generally better than the supermarkets, at the time of writing this review they are about £15.00 for this six pack (I have seen them in supermarkets at around the £30.00 mark for this number, so the Amazon price is a real bargain).
These filters come in a variety of pack sizes, from individual to four packs, this six pack, and eight, twelve and even twenty packs.
I really like this six pack size because we'll hopefully get just about a year out of it; so basically thats about £15 for the year, not too shabby!
Overall a very good product, they definitely work and do make a considerable difference to the taste of the water, your cuppa will never have tasted so good!