In Sacramento, even an inch of rain can lead to a much more complicated problem underground. The city is one of only two in California and four on the West Coast still operating a combined sewer system—a century-old design where stormwater and sewage flow through the same pipes. As climate challenges intensify, modernizing and maintaining the system is a 24/7 job. The history of Sacramento’s combined sewer system (CSS) stretches across 7,500 acres in neighborhoods like downtown, east Sacramento, Oak Park and Land Park. The system serves 300,000 residents, at least ten times the population when it was built. “These systems were never meant to keep up with the type of rainfall we’re seeing today,” said Carlos Eliason, a spokesperson for the city’s sewage operations.