Water trapped in wheels after washing bike
New bike - washed it the other day after a dirt/gravel ride and then parked it in the basement for a few days without touching it.
I took the wheels off last night to swap out different tires and noticed the front wheel made a slight sloshing noise in my hand. After I deflated and removed the tire, the rim bed was wet. I turned the wheel so that the valve hole was down (6 o'clock) and a small amount of water spilled out... maybe a tablespoon or two. Same story with the rear wheel.
These are stock Cannondale "CX 1.0" aluminum wheels that are tubeless ready, with rim tape installed. How/where is water getting in and is this something I should be concerned about? The bike hasn't been ridden in the rain, so it definitely got in when I washed it. I just used a garden hose & sponge, not a pressure washer or anything. Is it getting in through the valve stem somehow?
Any thoughts on this?