A burst or split supply line
Copper opens along a seam when it thaws; plastic usually lets go at a fitting.
Either way the house has turned into a garden hose that nobody is holding.
Do this first
Main off, lowest tap open, and the breaker off if the water heater is
electric. Then call. See leak & pipe repair.
Frozen, but not burst yet
One tap gives nothing on a cold morning while the rest of the house runs
fine. That is ice in a pipe — and it matters, because pipes usually burst on
the thaw, not on the freeze. Right now you still have a choice.
Do this first
Open the tap it feeds so meltwater has somewhere to go. Warm the area with a
hair dryer or space heater kept clear of anything that burns — never an open
flame — and stay near the shut-off as it comes back.
Sewage or a main line backing up
When the main drain is blocked, everything you run indoors has nowhere to go
but back out of the lowest opening — usually a basement floor drain or a
downstairs shower.
Do this first
Stop using water completely. No flushing, no dishwasher, no laundry — one wash
cycle can put a bathtub's worth into the basement. Keep people and pets out of
it. See drain cleaning.
Water coming through a ceiling
A sagging, bulging patch of drywall is holding far more water than it looks
like, and when it finally lets go it brings the whole sheet down with it.
Do this first
Water off, power off to that room's lights at the panel, a pail underneath —
then pierce the low point of the bulge with a screwdriver so it drains where
you want it rather than where it chooses.
A water heater letting go
A tank seeping from the bottom seam has rusted through. That one is not going
to be repaired, it is going to be replaced — the only question is how much
water it puts on the floor first.
Do this first
Power or fuel off, cold inlet valve at the top closed, then call. Be careful
around it: what is in that tank is still scalding. See
water heaters.
The sump is rising
In a spring melt or a hard rain off the bay, the pit fills faster than a tired
pump can empty it. Nine times out of ten the pump is not the fault: the float
is hung up on the side of the pit, or the discharge line outside is frozen or
plugged.
Do this first
Check the float swings free and the outside outlet is clear. If the pump hums
but nothing moves, unplug it rather than letting it cook, and call. See
pumps & well systems.