The Brita cartridges are expensive. From 3 to 6 euro per each. There is possible to cut this price 5 times less, so one cartridge will cost you 0.50-1 euro. The point is with refilling, of course. Main active filtering material is activated charcoal, which is easy and cheap for buy. Ebay, amazon, local adverts pages... Name it. Here I show you my solution of refilling. Probably is not perfect, but is quite enough for such purpose and it's working. If you have better suggestion, just let me know, I'm open to any advise or reasonable discussion.