This required filter is used to control tastes and eliminate odors from your drinking water. This filter should only be used for the K5 Drinking Water System. After 500 gallons of water has been dispensed through the faucet the MACguard filter will shut off to alert you that the filter needs to be replaced. This signals the need to change the pre-filter(purple) and this filter(orange). So that you can have reverse osmosis water again from your system.