I was drinking about a gallon of water a day and still felt thirsty and dehydrated - dry mouth, dry skin, dry eyes.(I'm 5'2", 115 pounds, so I should only need about 50 ounces per day). I read the Water Cure and started following the protocol. I'm now drinking around 64 ounces a day and have no problems with dehydration.
Good luck to you in you journey to quit smoking. My husband quit several years ago. It wasn't pretty, but we made it through OK.