I have washed my GW4 Classic with tap water many times over the course of 2.5 years. Its still going strong.
Samsung has tested the watch in fresh water. Swimming pool water is chlorinated and could potentially harm the watch. I would recommend not to, but have seen people posting questions on swimming pool length, voice callouts, settings, etc, so I assume that some do use it in a swimming pool.
If there is any water damage, then its not covered by the warranty.
If you do use it, enable Water lock so that the screen will not turn on or actions get executed due to random touches.
Also wash off the watch with clean tap water after coming out of the pool.
