Inside Philadelphia's New Water Management System

"Cities can spend billions maintaining and upgrading this antiquated gray infrastructure -- or they can follow Philadelphia's lead and turn instead to green infrastructure. The principle is simple: instead of struggling to cope with the volume of water rushing through the sewers, prevent it from getting there in the first place by capturing it and filtering it slowly and naturally through the soil."

The city plans to make on third of its surfaces more permeable to water over the next 25 years.