Fear of dehydration on Yom Kippur

It’s hard for me to answer. You need to ask a doctor (preferably a very religious one) what his opinion is. That’s what determines it. If the doctor says to drink, you should ask him if less than a certain amount is also okay. If so – that’s better. If not – you should drink as usual. Of course, don’t take any risks. But mere unpleasantness doesn’t allow it. Regarding the pill, if you can do without water, that is better. If not, and the pill is very medically necessary, then it is definitely advisable to taint the water. The poskim wrote that a small taint (a little soap) is enough for the taste and bitterness to be felt. It should not reach a point where you vomit from it. Even dissolving the pill itself if it tastes bitter (try it before fasting) can taint the water sufficiently. If you can sleep at home and not go to the temple and that will save the fast (and it was written in the Shashak on behalf of the Gershonites and the Hatas that even if it prevents drinking less than a shiur) – that is better.