Unlike water pipes, always full because of the pressure used to deliver water into homes, sewer pipes are rarely full when wastewater is flowing from homes to the sewage treatment plant. When water pipes break, crack or are broken, they leak water out; sewer systems, on the other hand, allow groundwater and stormwater to leak in.
When groundwater or stormwater leak into the sewer system, it takes up extra space that could be carrying wastewater. If the pipes become overloaded, raw sewage may overflow at points throughout the sewer system before it reaches the treatment plant.
