ItcheSrulik -“Boich svara time.
The general klal with d’rabbanans is that you can ignore them b’kum v’aseh for a choleh she’en bo sakana and kal v’chomer b’shev v’al ta’aseh. Dehydration is considered a choleh she’en bo sakana for the rabbinic fast days, so why not for netilas yadayim as well?”
Yes you said it. A Boich Svara.
Dehydration at a certain level is Sakonas Nefoshos. Unless you’re an expert in medicine you probably don’t know the difference between dangerous dehydration and not -so any level of dehydration is a Sofek Sakana.