The Vortex Water Revitalizer should ALWAYS be the last mode of water treatment in order to experience all of the benefits it offers, so it should always be installed AFTER your existing water treatment system.
If you have an under or over the counter water treatment system you can install a Vortex Water Revitalizer for Filters after it. You can also install a Whole House Vortex Water Revitalizer to treat the water throughout your entire home and benefit the environment, in addition to the Vortex Water Revitalizer for Filters.
If you have a whole house filter or water treatment system, you will need to install a Whole House Vortex Water Revitalizer after it.