Creatine monohydrate has a very low bioavailability. The majority of your dose will sit in subcutaneous water. The amount of creatine that your muscle cells actually absorb is small and IMO the amount you will lose by dehydrating yourself is negligible. As it has been said, dehydration itself is much worse than losing a little creatine. Just as a side note, creatine is not that effective. Even if you did lose some creatine in this manor you would never, never know the difference.