Marcus Hiles has observed that architectural trends are extending outdoors and towards designs that boast low maintenance and high style. The demand for open-air spaces that are sustainable and reduce costs is being satisfied through eco-friendly, conservation-minded processes like rainwater/graywater harvesting and permeable pavement. Rainwater harvesting utilizes a rooftop collection system that redirects moisture from the air into well storage to be treated and repurposed on-site. Graywater takes previously used domestic wastewater and recirculates it around the home and property for rest rooms and other non-drinking purposes, cutting the need for sterilization and fresh water. The seemingly new 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 lowers runoff and pollution, manages the flow of storm water running into gutters and drains, maintains local groundwater supplies, and can even provide a skid resistant surface for walkways, patios and driveways. There are many attractive designs and looks for permeable pavement, often incorporating crushed stone, brick, and recycled concrete.