My surgeon said you should get 32 to 64 ounces of water a day. That old rule about 8 8-oz glasses every day for every person is a myth. If drinking that much water works for you, and you feel better drinking it, then great, you should keep drinking it! But if you are in good health, and not working in high temperatures, your body does not need that much water. Plus remember your food contains water too. It's pretty clearly not working for you, so I think you should feel safe in dialing back as long as you don't go below 32 ounces.

snopes.com: Eight Glasses of Water a Day