Does using a home water treatment device guarantee that my water is safe?

No, the EPA does not recommend home treatment devices as a substitute for public water treatment because of the difficulty in monitoring their performance.  Home treatment devices are not tested or regulated by the federal government.  Some, however, are tested by independent laboratories.  If you want to use a water treatment device, carefully choose one according to the water conditions in your area.  Also be aware that a device needs to be properly maintained or it could cause water quality problems.