I'm reading an excellent book right now called "If it's not food, don't eat it" and on page 214, I read the following statement:
Many people who are ill and have a toxic, weakened system find that they can't seem to get enough water and are always thirsty. Once they start eating an abundance of high-water content foods such as fruits and vegetables, drinking juices and herbal teas, thier water needs are satisfied to a degree, and they drink much less water as a result."
I'm not saying that you are ill, but I do believe that it is a detox symptom. She gives good advice on how to deal with it.