Actually pond water has been on/in the ground much longer so it will usually have a lot more dissolved minerals in it. Here is a link to learn more. pond water
All water is H2O. No difference in the water at all. There are different things living in a pond that don't live in a raindrop, but all water returns to the sky and falls again.
The difference between pond water and rain water is that they contain different kind of pollutant in it.