Water on the surface

17. When it rains, all of the water may not go into the ground. Some of it may stay on the surface.

Water staying at surface

18. Water which stays on the surface will either lie in one place, if the land is flat, or it will run along the surface, if the land is hilly.

Water at surface: staying or running along

19. The water that lies on the surface is called surface water. The water that runs along the surface is called run- on water.