Stairs are composed of a tread (the upper horizontal part of a step) and a riser (the upright member between two stair treads). Waterfall installation attaches carpet to two points on each step (one at the back of the tread and one at the bottom of each riser). This type of installation extends the life of carpet on stairs. When the carpet on the treads become worn, they can be taken up, reversed, and reinstalled with the worn areas placed over the risers.