Philadelphia draws some praise from the Christian Science Monitor for using "green" strategies to keep rainwater from becoming polluted as it runs through the gutters and back into the creeks and rivers. Green infrastructure mimics how nature handles rainwater through the use of porous surfaces, rather than impervious surfaces like roadways. These techniques are decentralized. Instead of one facility or large underground tank to store water when a big storm hits, the idea is to eliminate the need for such storage through the use of green rooftops, roadside plantings, carefully landscaped parks, rain gardens, rain barrels, and other swatches of nature