If it is only in one vent you need to first eliminate the possibility of an interior source such as over watering a house plant a leaking aquarium or someone spilling water nearby.
Water in floor vents.
Afterwards metal or plastic vents can air dry or be wiped dry with a clean dry rag or paper towel.
The water in the ducts can initiate the growth of mold.
The old ducts probably rusted away from the water seepage so someone simply removed the rusted material which left a round tunnel for the return.
No they have standing water and a natural humidifier.
Each time the heating or cooling system operates the air moving through the ducts can blast millions of mold spores throughout the house.
What is the best way to fix this situation.
Water in buried heating and cooling ducts can cause serious health problems.
In this room the two floor vents fill with water when we get rain.
If you see water in any vent you should examine all of the other boots and ducts for water.
One vent has completely corroded on the bottom then and the ground water seeps in and fills that whole section of vents.
I bought this home 1 yr ago and was a flip home.
Wet your tool with water apply soap to it and clean each vent.
Anonymous i have water in my floor ac air vents.
Only when i run the dish washer and run the washing machine.
Use a dish cleaning tool like a scrub brush or sponge to clean the slats of the vent and other narrow crevices.
My vents new by.
I have been told to fill the vents with concrete or expanding foam and abandon them lift my furnace tap into the down flow and put a new vent in the ceiling in that room and even get.