Musty Smell With No Visible Water

• A slow supply leak wetting framing and insulation inside a wall
• Water under a tile bed or vinyl floor with nowhere to evaporate
• A shower pan or curb leaking into the substrate
• A drain leak beneath a cabinet or behind a toilet
• Air handler condensate saturating a closet floor or return chase
• High indoor humidity and poor circulation in a closed area

Walk the space and note exactly where the odor is strongest — at floor level, at an outlet, inside a closet, near a return vent. Odor concentrates where air moves out of the wet cavity, which makes it a surprisingly good pointer.

Then check the meter with everything off. Continuous loss plus localized odor is a strong combination pointing at concealed pressurized water.

When the odor is persistent, localized rather than general, and does not improve with ventilation and dehumidification. General mustiness across a whole house in August is more likely a humidity and airflow issue than a pipe.

Moisture readings across the suspected area, thermal scanning to find the boundary of the wet zone, and isolation testing to establish whether pressurized water is involved. Locating the moisture matters even when the source turns out not to be a pipe, because saturated material has to be dried either way.