I think some hold that to prevent thirst is considered לצמאו so would require a bracha, but if if the hydration was for medical purposes, if the person wasn’t otherwise נהנה, no bracha.
Your idea that any benefit requires a bracha is clearly wrong; using water in a case of חנקתיה אומצא (and all of the cases the poskim say are comparable) is benefiting from the water, yet there’s no bracha.