The U.S. Census Bureau projects that the U.S. population will grow by 50 million people, or approximately 18 percent, between 2000 and 2020. Many communities are asking where and how they can accommodate this growth while maintaining and improving their water resources. Some communities have interpreted water-quality research to mean that low-density development will best protect water resources. To more fully explore this issue, the U.S. Environmental Protection Agency modeled three scenarios of different densities at three scales -- one-acre level, lot level, and watershed level -- and at three different time series build-out examples to examine the premise that lower-density development is always better for water quality. This analysis demonstrated:

• The higher-density scenarios generate less storm water runoff per house at all scales -- one acre, lot, and watershed -- and time series build-out examples;
• For the same amount of development, higher-density development produces less runoff and less impervious cover than low-density development; and
• For a given amount of growth, lower-density development impacts more of the watershed.

Taken together, these findings indicate that low-density development may not always be the preferred strategy for protecting water resources. Higher densities may better protect water quality -- especially at the lot and watershed levels. To accommodate the same number of houses, denser developments consume less land than lower density developments. Consuming less land means creating less impervious cover in the watershed. EPA believes that increasing development densities is one strategy communities can use to minimize regional water quality impacts. To fully protect water resources, communities need to employ a wide range of land use strategies, based on local factors, including building a range of development densities, incorporating adequate open space, preserving critical ecological and buffer areas, and minimizing land disturbance. Read more about this report or find out how to order print copies click HERE.