The TO1 is a carbon wrapped cartridge for the industry’s best-selling Whole House water filter, Model U25. The TO1 also fits OMNI Whole House filters OB1 and OB5 as well as the older models, R12, R14 and Omni Regular Whole House water filters. By reducing sediment and chlorine in incoming water, the TO1 provides clean water to every faucet and appliance in your house.