I’m trying to troubleshoot a very strange moisture issue and would appreciate input from anyone experienced with building science, hygrothermal behavior, or moisture diagnostics.
Since July, small puddles of clear, cold water have randomly appeared directly on top of my flooring. It has happened on every floor, in different rooms and locations.
The important part is that it still happens when indoor RH is below 50%, so I’m not convinced this is simply general indoor condensation.
House/details
~2,000 sq. ft.
Vinyl flooring installed in 2023
Multi-zone mini-split heat pumps installed in 2024
5 outdoor units / 8 indoor units
Puddles appear directly on the floor surface
Water feels cold
No obvious plumbing or HVAC condensate leak
Occasionally slightly yellowish with a musty smell
Investigation so far
Plumbers and HVAC technicians have investigated without finding a source.
A professional water restoration/moisture investigation company also scanned the house using thermal/moisture equipment. They found no elevated moisture or water in the areas inspected, including the subfloor.
The strange part is that I can have a puddle on the floor, but there is no obvious moisture signature underneath or around it when investigated.
I’ve also monitored humidity closely. The puddles still occur with RH below 50%.
I tested some samples as well. Tap water and AC condensate were around 30 ppm TDS, while one puddle sample measured approximately 418 ppm. I realize TDS isn’t enough to identify the source.
I even placed cameras in previous puddle locations to rule out accidental spills. Naturally, the puddles stopped appearing wherever I put the cameras. 😂 We have two kids, so accidental spills were one of the first possibilities I considered.
Building-science question
What mechanism could cause cold liquid water to appear at the finished floor surface without detectable moisture in the subfloor, particularly when indoor RH is below 50%?
Could this involve:
Localized surface temperature/dew point conditions?
Air leakage or pressure-driven moisture transport?
Vapor movement through the floor/wall assembly?
Moisture migration along an unexpected pathway?
Intermittent exterior water intrusion?
Flooring or adhesive behavior?
Something that a thermal/moisture scan would miss?
If this were your house, what diagnostic test would you do next to determine the actual source/pathway of the water?
I’m looking for ways to prove where the water is coming from, rather than simply treating the symptoms.