can you get a replacement Airpod if one gets water damage

Yes. Check this out for lots of helpful information regarding AirPods service at Apple.

Specifically, as to your question, concerning one AirPods Pro damaged by water, if one or both of your AirPods or Charging Case need replacement because of physical damage, you can replace each damaged item for an out-of-warranty fee. Physical (water) damage to an AirPod is not covered by the regular one-year warranty, as I understand it. If your AirPods are covered by AppleCare+ for Headphones, however, you’ll pay only an AppleCare+ service fee per incident of $29 (each incident). Without AppleCare+ for headphones, there is an out-of-warranty fee of $89 each to replace a damaged AirPod Pro.

Good luck!

-- JDee