My favorite is Ultrapure Water (UPW) [0]. It's so pure, that it is used a a stringent. I watched video about one of those underground subatomic particle experiments where they use UPW. One of the technicians accidentally let his hair get wet, and it immediately "bleached" his hair.
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.
I don’t understand why it would bleach the hair? Theoretically couldn’t you drink this? It’s just water that’s free of contaminates like viruses, bacteria, etc?
Ultra pure water generates a very strong osmotic gradient in that it will simultaneously explode cells as the pure water rushes in to reduce particle count inside a cell while at the same time drawing out any free particles.
Another way to think about it is that UPW is an acid with a concentration of 55 Moles/liter.
[0]https://en.wikipedia.org/wiki/Ultrapure_water