This is a great question and one that should be considered carefully by athletes and active individuals. Creatine causes your muscles to retain extra water, therefore your body will require additional fluids. It is easier to become dehydrated while taking creatine. This is especially true if you are performing rigorous activity (working outdoors, sports practice, etc) and/or if the weather is hot. I would recommend increasing your water intake by at least 20-25%. For an average size active male, I would recommend drinking at 1-2 gallons of water per day.

One good indicator of your hydration level is the color of your urine. It should be clear throughout the day (it may be yellow in the morning or right after you take a multivitamin). If your urine begins to look yellow, it means you are already dehydrated! If that happens, hydrate yourself and increase your water intake the next day.

Some studies also suggest that creatine places extra work on your kidneys. Consuming plenty of water helps keep your kidneys flushed and performing at their optimal levels.