This parking lot is made of porous pavement that allows rainwater (and snow as shown at top left) to filter through two-and-a-half feet of permeable materials including porous asphalt and crushed stone. If you have a water bottle, try pouring some of the water on the surface and observe what happens. The permeable pavement filters pollutants and allows stormwater to percolate slowly into the ground, reducing the rate and volume of stormwater runoff.