Re: opinions from parents of Asperger's kids
He was over stimulated and working it through the best way he knew how. It is very common for ASD kids to act differently in situations that overwhelm them. You just need to find a way to redirect the behavior when it's happening. Pull him away from the water and wrap him in his towel and apply deep pressure to his body with squeezes ( hugs ). Redirect the singing by singing with him at an appropriate level bringing his attention to you and he may copy it. He just needs to release all this energy his brain is giving off due to the overstimulation.
There is a great book called The Out of Sync Child which talks a lot about the sensory stuff our kids go through. I highly recommend it if you haven't read it already.
He is still very young and will learn how to cope better as he gets older but in the mean time the key is just constant redirection and giving him a more appropriate outlet for the release of that energy.