Place a bucket or large pan underneath your OmniFilter water filtration system to catch any excess water that may spill.
Turn the cutoff valve handle to the water line, which is usually located under the sink, off. If there is no cutoff valve under the sink, shut the water off to the entire house.
Press the blue pressure relief button located on top of the OmniFilter water filtration system down for at least three seconds. A small amount of water may be released from the filter. Allow the bucket or pan to catch it.
Unscrew the bottom portion of the water filtration system with the blue tank wrench that came with your OmniFilter water filtration system. Turn the tank wrench clockwise.
Pour any water currently located in the tank you just unscrewed out into your bucket or large pan.
Discard the old water filter cartridge.
Wipe the tank out with the clean cloth. Wipe the O-ring with the clean cloth.
Place the new water filter cartridge into the tank, ensuring the cartridge fits over the post on the bottom of the tank.
Replace the O-ring back on top of the tank.
Screw the tank back onto the rest of the OmniFilter water filtration system. Tighten it as much as possible by hand.
Turn the water line's valve handle on, slowly.
Press the pressure relief button until the tank fills with water.
Turn on the water in your sink on for about 10 seconds to allow any accumulated air to flow through, if you have the below-the-sink OmniFilter water filtration system model.
Discard any water collected in the bucket or pan. Wash the bucket or pan.