There is some basis to this claim, razor-thin though it might be.
Certain humid weather patterns can extend the range of VHF and UHF signals,
in a phenomenon known as "tropospheric ducting". So, if you had an
industrial-strength humidifier that could fill a few thousand cubic feet of
air with moisture, you might get a stronger WiFi link. (A pocket-sized
version of this humidifier will be available, along with a portable
nuclear-fusion power source, in your dreams.)
The water will not filter out ambient electrical noise, but a stronger
Wi-Fi signal *might* cope with ambient noise better since the data rate,
and thus error correction, would be enhanced. Add some - highly conductive
mineral particle sparkle&flash glitter filler - to your water and you have
NoSweat GetWet FancySounding WiFi Super Juice (with Cherry Scent)!
On the other hand, you might also get your computer wet, and laboratory
experiments consistently show at least a 94.5% reduction in WiFi efficiency
when the laptop is exposed and submerged in depths of more than 2" of water
- especially if the water contains trace levels of Phosphoric Sulfate
Dioxide (O2PS, also known as OOPS). I challenge anyone to defeat this
claim through empirical experimentation.
Mike