The Louisiana Department of Health and Hospitals has issued a weird warning: if you have to irrigate your sinuses with water for some medical reason, don’t use tap water. The reason: your brains may get eaten by the Naegleria fowleri.
Water that you drink is quite all right—even if it contains the bacteria, it will be destroyed when it reaches the stomach and the body’s digestive juices.
But beware if you intend to put water up your nose! This channel is not intended for water (or other food), and does not have the same defense systems as our digestive system does.
The amoeba attacks your nervous system, and can pretty soon leave you dead! Fortunately, the way around is pretty simple: just boil the water to kill the bug!
(My gripe with the article: no source information! No links, whatsoever. Terrible.)