The AquaClean filter by Philips removes the smallest limescale particles from the tap water. You can prevent limescale in your coffee machine that way, and retain the best quality for every cup of coffee. You should replace the Philips water filter every 3 months. If you keep up with this work, you just have to descale your Philips or Saeco fully automatic coffee machine once every half year. If you purchase 4 AquaClean water filters right away, you'll have enough for the coming year.