The Number One Menace - The Ripple Effect: The Fate of Freshwater in the Twenty-First Century - page 39

Cities face another set of runoff problems even more daunting than those faced by
rural communities. With much of their surface area paved, cities do not absorb pre-
cipitation well. The thousands of pipes, valves, and pumps of city sewers are often old,
leaky, and overwhelmed, especially during an intense storm burst or a prolonged rain.
Furthermore, the demand on city systems to separate water from human and industri-
al effluent is much higher than on rural systems. Sewage treatment requires enormous
amounts of energy, which is costly and adds to climate change—which ultimately cre-
ates more runoff. Most of the nation's sewer network was built in the nineteenth and
twentieth centuries and has been compared to a ruptured appendix—an overburdened
system that is struggling to function and remain clean.