As mentioned before in our filters, membranes and DI FAQ pages, the filters need to be replaced when: Pre-filters should be replaced at least annually. This includes the 10 Micron Sediment filter, the 5 Micron Carbon block or Catalytic Carbon filter and the 1 Micron Carbon filter (if one is installed.) The sediment filter does tend to look like it's getting dirtier faster then others. This is normal. Since it's the first filter, it's removing most of the heavy particulate matter. If water production slows, see it if's the sediment filter first. The RO membrane needs to be replaced every 3-5 years. If your water is hard and you do not have a softener, then you may need a larger fast flush flow restrictor. This is just a temporary measure and will only slow down the scaling process. * The DI is based upon how well the RO removes TDS from the water. *** Though we recommend replacing it annually, it may need to be changed more or less often. Go by TDS readings instead. If the TDS is above 5 PPM {stabilized}, then you should replace the DI. * See www.filmtec.com for warranty details * See our DI FAQ page for calculations