Treat spring water before drinking and don't drink the river water. You must be alert for this, because a flash flood may travel down the watershed to you even though you were not rained on.
Flash floods make roadway dips potential death traps.
If you are caught in high water on the road, drive slowly to avoid stalling your engine. Campers must also take precautions against flash flooding. Do not camp in washes and arroyos, because they could turn into swirling rivers while you sleep. And you can't count on having the warning of raindrops to wake you. To avoid them, stay on trails after dark and use a flashlight, and avoid bushes and damp areas.