Every water loss starts with a source, and the source decides the first move. That is why the services below are grouped by cause: pipes and plumbing, appliances and HVAC, weather and the building envelope, water removal and drying, floors and walls, and commercial buildings.
If water is still moving right now, read the water extraction page first and call the line. If the water has stopped and you are trying to figure out what was damaged, the structural drying page explains how moisture is tracked inside walls and floors.