Marcus Hiles notes that architectural trends are extending to include outdoor designs that boast low maintenance and high style. This demand for open-air spaces that are sustainable and reduce costs is rapidly rising through eco-friendly, conservation-minded processes like rainwater/graywater harvesting and permeable pavement. Rainwater harvesting Utilizes a rooftop collection system which redirects moisture from the air for storage in a well to be treated and repurposed on-site, and graywater takes previously used domestic wastewater and recirculates it around the home for rest rooms and other non-drinking purposes, cutting the need for fresh water and reducing the amount of sterilization. The seemingly novel idea of permeable paving actually dates back thousands of years to the time when people first built roads by putting stones in beds over the ground. The process allows rain to pass through small openings between four layers of filtration (paving material, gravel, fabric, sand) before being absorbed by the dirt below. This process lowers runoff and pollution, manages the flow of storm water to gutters and drains, replenishes local groundwater supplies and can even provide a skid resistant surface for walkways, patios and driveways. There are many attractive patterns for permeable paving, often incorporating crushed stone, brick, and recycled concrete.