Water is an essential component of human life and an important resource for the natural environment. It is also a primary concern when designing and constructing new facilities or renovating old structures. The whole point of a building facade is to keep rain and other precipitation from compromising the interior structure and finishes. Water also has to be dealt with on a site-wide basis, as large puddles are not only undesireable but can be harmful to the foundation and hamper access to the site itself. For these reasons, we have a history of designing buildings and sites to take the water "away". Roof gutter systems lead to asphalt parking lots which slope appropriately to gather all water falling on the site and funnel it neatly to a storm drain, which connects to the municipal sewage system, which connects to a local stream or river and ultimately the ocean. This system of stormwater management, when applied on such a large scale, can have dramatic effects on local ecosystems and requires extremely expensive utility systems. The two main issues with storm water control are quality and quantity. The quality of stormwater runoff, after it has gathered dirt, oil and other inorganic compounds from a parking lot or other paved surface, can be toxic to local plant and animal life and can compromise whole ecosystems if released straight into local water sources. The quantity of stormwater runoff is equally important because large and sudden influxes of stormwater from large nonpervious surfaces causes erosion and other damage to local watersheds.
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