Example: the water heater leak that kept smelling two years later

The situation

Illustrative example. Not a real job or customer.

A family's water heater, in a utility room next to a finished basement rec room, split at the bottom tank seam overnight. By morning water had spread under the wall into the carpeted rec room. A relative helped pull back the carpet edge and ran box fans for three days. The carpet felt dry, the family put the room back together, and a new water heater was installed. About a year later a musty smell appeared in the rec room, getting stronger each summer.

1. The family first assumes the new water heater is leaking and has a plumber check it; it is fine.
2. They lift the carpet in the corner nearest the utility room. The pad underneath is stained dark and smells strongly. The slab beneath feels cool and damp.
3. Removing the baseboard on the shared wall reveals the bottom of the drywall stained and soft for a few inches up.
4. A moisture meter shows elevated readings in the drywall and along the bottom plate of the wall.
5. They have the affected drywall cut out above the stain line, the pad and tack strip removed in that section, and the slab and framing dried with dehumidification until readings normalize.
6. Light surface growth on the back of the removed drywall and on the bottom plate is cleaned once dry; the plate is sound.
7. New drywall, pad and the original carpet, which was cleaned and smelled fine once the pad was gone, are reinstalled.

The musty odor does not return through the following summer. The family keeps a leak alarm next to the water heater and replaces supply hoses on a schedule.