Developments in architecture have moved to hot outdoor designs that are supposed to be low maintenance and stylish. Marcus Hiles has seen the increase in demand for open-air spaces that are sustainable and also reduce expenses. Ecological, conservation-minded choices such as rainwater/graywater harvesting and permeable pavement are popular methods. Using a rooftop collection structure, rainwater harvesting sends moisture from the air for storage in a well to be treated and reused on-site; graywater takes home wastewater used before and sends it for rest rooms and non-drinking purposes, reducing the need for fresh water and dropping the amount of purification. A special idea for environmentally minded construction, permeable paving, actually goes back thousands of years to the time when people first made roads by putting stones in beds over the ground. The technique allows the rain to pass through small openings between four layers of filtration (paving material, gravel, fabric, sand) before becoming absorbed by the earth below. Its advantages include lowering runoff and pollution, controlling the flow of storm water to gutters and drains, replenishing local groundwater supplies and providing a skid resistant surface for walkways, patios and driveways; their many attractive patterns often incorporate crushed stone, brick, and recycled concrete.