Stringent just means something is strict, as in the standards for making UPW. Nothing is “used as a stringent.” UPW also doesn’t immediately bleach hair, it w

Stringent just means something is strict, as in the standards for making UPW. Nothing is “used as a stringent.” UPW also doesn’t immediately bleach hair, it would have to be a pretty prolonged heavy stream. Mostly UPW is pain in the ass because it corrodes metallic pipes, but is pretty harmless to people unless you really have massive amounts. One of the reasons it’s harmless is because the moment it touches you it isn’t really ultra pure anymore, it really takes parts per million to become not UPW.