Protip: add a few drops of milk to water to make lasers show up better. You want particulates to scatter the light, and little globules of fat do just fine.

Here you can see total internal reflection of the laser off of the surface of the water. The structure of the beam is probably because I didn’t stir the water, so the milk was only mixing due to the residual motion of it and the water. You can see it’s settled a bit at the bottom.