I think it could be related. The following is an excerpt from Wikipedia. So I won't pretend to fully understand a lot about creatine, but if it causes more water to go into the muscles, then your body might require more water intake whilst using it.
"Some studies have shown that creatine supplementation increases both total and fat-free body mass, though it is difficult to say how much of this is due to the training effect. Since body mass gains of about 1 kg can occur in a week's time, several studies suggest that the gain is simply due to greater water retention inside the muscle cells. However, studies into the long-term effect of creatine supplementation suggest that body mass gains cannot be explained by increases in intracellular water alone. In the longer term, the increase in total body water is reported to be proportional to the weight gains, which means that the percentage of total body water is not significantly changed. The magnitude of the weight gains during training over a period of several weeks argue against the water-retention theory.
It is possible that the initial increase in intracellular water increases osmotic pressure, which in turn stimulates protein synthesis. A few studies have reported changes in the nitrogen balance during creatine supplementation, suggesting that creatine increases protein synthesis and/or decreases protein breakdown. Again, while hypothesized, this remains unproven."