Spark image

Transparency of water


Some time ago a boy drowned in Los Angeles and the police couldn't find him. However, the boy turned up in the pool a couple of days later. The police claim that the pool was dirty and when they looked in the pool, it looked like they were looking at the bottom when in fact, they really couldn't see the bottom where the boy was. How does this work?


Water is transparent and that is why you can see through it. Light passing through water is absorbed slightly but a much more important thing is the scattering of the light as it meets small particles (even down to molecular size) in the water. If the water is dirty not much light will reach the bottom of the pond. Therefore not much light will be reflected back and there might well be so little that whatever is on the bottom of the pond will not be visible to someone looking in from above.

© Keith Gibbs 2013