This is the most popular size for residential well water systems or whole house filtering. The 3/4" unit T2C filter unit is most often used in residential systems for filtering out sand and debris from well water systems and from old corroding city water lines. It may be used as a pre-filter before high-end water treatment systems.  When used in a residential system, it will help keep appliances and faucets clean of any debris or hard water deposits that may enter the residential water lines. The 1" filter unit can be used in irrigation, where there is not a heavy load of particles in the water supply or where some additional filtering is needed, such as for drip irrigation systems.