The first move is mechanical: close the main shutoff. Every gallon after that decision is a gallon that does not need drying, and the shutoff is the one tool every homeowner should be able to find in the dark. If water has reached outlets or appliances, cut power to those rooms at the breaker before wading in.
In the Hanover area, the first hour forks at the water source. Borough homes: main shutoff, photographs, the standard order. Township homes on wells: the pump breaker joins the shutoff on the checklist, because a split well line with the pump running is a well emptying itself into your yard and your electric bill at once. Photograph the pump's pressure gauge behavior if you can do it safely; in the fringe, that reading is the first diagnostic, and it is gone once the power is cut.
The second move is evidence: photographs of the failed line, the rooms, and the water's reach, taken before anything is moved or mopped. Insurers approve documented sudden losses; undocumented ones get argued. Note the time you found it and the time the water stopped.
The third move is the repair read: a split is a symptom with a cause (freeze, corrosion, pressure, age), and the repair visit should name the cause, because a patched effect with a live cause is next season's burst in a nearby section of the same run.
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