Being thirsty all the time is the most obvious sign of Diabetes!! Before you try to figure out if it is good or bad to drink lot of water, test your self (your Dr. would know).

Now, if you have eliminated diabetes: there is such a thing are drinking "too much water" and it is different for everyone depending on diet, weather, activity, etc. In my army days serving in the desert I would drink almost 20 liters (over 5 gallons!) in a day, but I was working my butt off in 45 C (~115 f) in a very dry environment. drinking and sweating that amount of water deplete our electrolytes and we would take "salt pills" which had electrolytes and other supplements.

For normal people like us, it is very hard to "drink too much"... So if you Dr. says you are ok (diabetes wise), then I wouldn't worry...