Your battery should be fine especially if it was a brief dip in the toilet. It thinks there’s water in the port probably because of a short between a couple pins in the port. Try some rubbing alcohol on a toothbrush to scrub inside the port. You can gently push the bristles into the port to scrub the inside. Let it dry for a couple minutes and then try to charge it. If it continues you’ll probably need a charge port replacement.
Thankfully the port is on a separate daughter board which means replacing it is pretty easy. The downside is it takes after the 1st gen pixel design in that the screen needs to be lifted off to get to it. You’ll need to be really careful about removing it but you should order a replacement screen to have on hand as it’s quite easy to break.