The whole point of thirst is to let us know when the body is in need of hydration. Drinking beyond thirst means that the body gets an excess of water that then must be eliminated which is just another "drain" on the available energies. So, if you are in touch with your thirst and you obey it, you should always have sufficient hydration to carry on the vital processes of the body but never a detrimental excess .
However, if you're not able to recognise thirst or if the signals just aren't there, you can never be sure whether to drink or not and can only guess.
A bit of experimentation may be useful here. Monitor the amount of water intake, the amount of urine expelled and note its color and smell, and then note any changes when you increase the water intake. Also notice how you feel before and after you have a drink. Did you get the impression that a need was satisfied?