@mhrps
All these replies are interesting....
However, maybe I misunderstood,
but I thought the original post says that he is not thirsty,
but does feel better when drinking water/fluids.
And the post asks, so how to tell how much to drink?
My answer, for me, is that if I have not peed in a few hours, then I slowly drink water and clear fluids,
until I do need to.
That way , for me, I know I am at least drinking a proper amount.
Whether or not it is going all the right places, of course, I do not know,
and would not be surprised if not, but I try to control the initial part, which I can.