The Short Answer
A waterfall countertop has a continuous piece of stone or surface material that runs from the top surface, turns 90 degrees at the end of an island or peninsula, and drops vertically to the floor. The result is a continuous 'waterfall' of material down the side. Waterfall edges are a high-end design element, most often specified in quartz or marble. The mitered joint at the top corner must be precisely matched for grain or pattern continuity, which is more challenging with natural stone. A waterfall edge on an island typically adds $500-$2,000+ to countertop cost.