My garage floor is wet, but I can't find a leak. Who do I call?
Usually, start with
Building moisture / water-intrusion professional
If the garage floor is repeatedly wet and there is no obvious plumbing leak or rainwater entry point, a water-intrusion or moisture professional can evaluate where the moisture is coming from and whether the condition is related to the slab, enclosure, or surrounding water conditions.
Change course if
The wet area is near plumbing, an appliance, or a water heater
A plumber may be relevant when a plumbing source is plausible.
The surface looks uniformly damp or develops moisture in humid weather
An HVAC or building-performance professional may be relevant when condensation is suspected.
The wetness follows rainfall
Drainage or waterproofing expertise may be relevant when exterior water conditions appear connected.
Who handles what
Water intrusion / moisture
Evaluates unexplained moisture patterns and helps identify likely entry or moisture pathways.
Plumbing
Evaluates pipes, fixtures, appliances, and other plumbing sources.
HVAC / building performance
Evaluates humidity, temperature, ventilation, and condensation conditions.
Drainage / waterproofing
Evaluates exterior water movement and water entry through the building enclosure.
What might be happening
A wet slab can result from liquid water entering the garage, a plumbing source, or moisture condensing on a cool surface. The appearance of the water alone may not distinguish among those possibilities.
Useful things to notice
When the wetness appears
Rainfall, humid weather, appliance use, or no obvious pattern can each be useful clues for a professional.
Whether the wetness has a clear edge or source point
A localized puddle differs from widespread surface dampness.
Whether walls or stored items also feel damp
Broader moisture conditions can help establish whether the issue extends beyond the slab surface.
Before you call
Photograph the wet area before drying it. Note recent weather, nearby plumbing or appliances, and whether the condition disappears and returns.
Before you fix the visible symptom
Coating, sealing, or covering a repeatedly wet slab before the moisture source is understood can conceal useful evidence and may create problems for finishes that depend on a dry substrate.
References
U.S. Environmental Protection Agency. Moisture Control Guidance for Building Design, Construction and Maintenance.
U.S. Environmental Protection Agency. Mold Course, Chapter 2: Moisture Problems.
ASTM International. ASTM F2659-23, Preliminary Evaluation of Comparative Moisture Condition of Concrete Floor Slabs.