Law enforcement: I have a question about taser guns?

I was watching something on television earlier, and a man was in a lake or pond trying to drown his child. When the police officers got to him in a boat, they were trying to stop him, but found it difficult for whatever reason. I think mostly because he was a really strong man. But my question is, and I know I am probably just being stupid, but can you use a taser gun on someone while they are in water without it causing harm or death?