While still on land, Lewis gives Zane a solid black earpiece to wear on the water. Later, Zane is wearing a mostly yellow earpiece, and the ear it's in changes.
Emma's mother's junior lifesaving certificate, earned when she was 12 years old, is made out to Lisa Gilbert. Gilbert is her married name. Of course, if it was never issued originally, Emma may have requested it in her mother's married name and not her maiden name in which she actually earned it.
In almost every episode, the lining of an underwater net is visible whenever there is an underwater scene. For example, in this episode, when Rikki saves Zane, the line of the net can be seen.