Why is my AC leaking water inside the house?

A central AC in a Houston summer pulls a surprising amount of water out of the air, well over a gallon an hour on a humid afternoon, and all of it has to run out through a condensate drain line that is usually a length of PVC pipe. That pipe grows algae, collects dust, and clogs, usually in July. When it does, the drain pan fills and overflows, and the first sign is water on the floor by the air handler, a stain on the ceiling under an attic unit, or the system switching itself off because the float switch tripped.

The fix is clearing the line and flushing it, and a technician will usually also check the pan for rust and the secondary drain for a clog. If the air handler is in the attic, the secondary pan under it is what stands between you and the ceiling, and if it has rusted through, that is the repair to make before the next clog.

The other causes are less common: a frozen coil melting into the pan faster than it can drain, a cracked pan, or a unit installed off-level. If the water appears only when the system is frozen, that is a different problem, and the thawing question is the one to read.