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
What Is The Difference Between pond Water And Rain 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.