It is installed on the main water supply. A key is required for easy replacement of the filter cartridge.

Close the water supply, vent the filter device from the vent, and then use the key to unscrew the canister. Remove the old filter and install the new one. Carefully screw the canister back on, ensuring that the hose (O-ring) does not come out of its position. Tighten it with the key, close the vent, and open the water supply.

It has no direction; it can be inserted from either side into the device.