Do I need to worry about mold issues when my basement floods? Home >> Water Restoration FAQ > Do I need to worry about mold issues when my basement floods? Yes. Leaving water sitting for over 48 hours will cause mold to set in. It is highly recommended that you call for assistance before 48 hours have passed. After two days, mold can set in and cause severe damage to your home by releasing harmful toxins in the area. If this has already occurred, call right away for help.