When I was in my 20s I realized I had lost the thirst signal. I never felt thirsty. I guessed this was because I lived a comfortable life and I had lost this signal in the noise of modern life.

So I set about deliberately retraining myself. I stopped drinking everything but water (and beer, because life) I'd exercise (and sweat) and then drink water. I retrained my body/mind to savour the pleasantness of drinking water when dehydrated and after a year of conscious effort I more or less recovered the sense of "thirst" and would pre-emptively desire drinking water.

We are pretty simple machines.