The expansion of a city into the countryside can be reduced through urban planning and building design. Also, a country?s best soils are often near large urban areas. Projects that promote compact urban form, encourage sustainable agriculture or maintain forest cover near cities can help preserve precious soil resources. Urban growth increases the demand for fresh water; while the infilling of wetlands, the destruction of aquifers, and water pollution reduce its availability. An effective way to maintain the quality and supply of fresh water for urban areas is to retain forest cover and reduce agricultural pollution in upstream areas. Materials used for urban construction include crushed rock, sand, wood, metals, etc. Eco-City projects that reduce road expansion or recycle construction materials can reduce the use of natural resources.