Whether you are using a public or private water supply, the only way to be sure your water is safe is to test it yourself.
(you; are using; a public or private water supply) (your water; is; safe) (the only way to be sure your water is safe; is; to test it yourself)
you your water the only way to be sure your water is safe
are using is is
a public or private water supply
safe
to test it yourself