Most people consider concrete to be impervious—after all, it’s used to make swimming pools and kitchen sinks. And most concrete is, indeed, nearly watertight. But a new kind of concrete that allows water to flow through virtually unimpeded is gaining popularity. Pervious concrete is being used mostly in the construction of parking lots, but also for sidewalks, bike paths, playgrounds, and erosion control. Pervious concrete pavement is not, however, suitable for areas subject to high traffic volumes or speeds.