they make both regular and waterproof versions, but i like the regular a little better. my lashes stay separated better with it.
i have very long eyelashes (they more or less touch my eyebrows when my eyes are open wide) and chanel is the only thing that stops them from sticking together in big clumps. because of the brush (it's got little nylon spines instead of thick bristles), it separates my lashes out like nothing else and makes sure they ALL get coated with mascara. it beats diorshow hands-down.