What begins as a slow drain can cascade into a disaster. Standing water in sinks and tubs becomes a breeding ground for bacteria, mold, and drain flies (psychodidae). Overflowing toilets or sewer backups bring black water—classified as Category 3 water loss by restoration professionals—which contains pathogens like E. coli , hepatitis A, and norovirus. Structural damage follows: water seeps into subflooring, drywall, and foundations, leading to rot and costly repairs.