Sewer backups are one of the most unpleasant and costly problems a NYC homeowner can face. Prevention starts with understanding what causes backups: tree root intrusion, grease buildup, aging pipes, and overwhelmed combined sewers during heavy rain. Key prevention tips include installing a backwater valve, scheduling annual sewer cleaning, avoiding flushing non-degradable items, properly disposing of cooking grease, keeping trees trimmed near sewer lines, and knowing the location and condition of your sewer line. NYC properties connected to combined sewers are at higher risk during heavy rainfall events.