 Older cities, when they built their sewer systems, they were designed to collect both wastewater from homes and businesses, but also stormwater. So the systems are designed to collect both. The sewers in Providence are that older kind, which means they have to handle both the stuff we flush down the toilet or the drain and our rainwater, all mixed up in the same pipes. That makes the system more likely to get overwhelmed if it rains a lot. And if the system gets overwhelmed, the extra water will get stuck in the pipes and back up into people's homes if it's not released somehow.