[FrankJ]

Originally Posted by GeeTwo

Quite the contrary. While in-place flash floods are possible when you actually have more than 6" of rain in 6 hours (e.g. here on the Gulf Coast), most flash flooding is the result of rapidly moving water. Rapidly moving water picks up silt, sand, and even rocks, houses, and bridges if it's moving fast enough. If you check out the Wikipedia page on flash floods today, you will find three pictures. All of them show dirty water.

That would be flood water. (your definition) And you are correct It picks up stuff from places that regular run off does not so it tends to be dirtier. Especially when it overwhelms cache basins. Rain water is the stuff that comes out the sky and becomes flood water when it reaches the ground.