Quote Originally Posted by dragonrage
yes they speak specifically about sea water. Regular water is not a threat. Think about it even if they didn't mention it. It would be very confusing watching the fight between Luffy and Crocodile, remember in the second and final fight, at the begining he use a barrel of water to counter Crocodile's sand ability, and when Crocodile tried to break the barrel he drank the whole thing. Also i mean it would be silly, everytime you drink a glass of water you get weak. Also the bars of the cage that held them as well as the stick Smoker carries are said to be made of some type of solidify sea water.

But this brings up an interesting question, What about fresh water lakes, in other words drinking water lakes. Would his powers be disabled then. Would Luffy finally be able to swim again? heemmm?
I agree with you that it is usually sea water that poses the problem to devil fruit users but you have to remember that Luffy couldn't swim in the seas of Skypiea either. I just guess its a general weakness to large water bodies.