The tag stopped working after getting wet
Dry it completely and test again, because those are two different outcomes. Water sitting on a tag attenuates the field and the tag recovers. Water that got inside destroys the substrate, and the tag then fails mechanically rather than electrically.
Two different things
Water on the outside attenuates the field somewhat. A wet tag typically still reads, at a reduced distance, and returns to normal once dry.
Water on the inside destroys the tag as an object. The substrate swells, layers separate, the adhesive releases, and the antenna is left unsupported and free to deform.
The second is permanent and the first is not, so the first thing to establish is which one you have.
Dry it and retest
Let it dry completely, at room temperature, for longer than seems necessary. Moisture trapped between layers takes far longer to leave than a wet surface.
Do not apply heat to speed it up. Heat plus a damp laminate is how a tag delaminates, and a hairdryer has ended more tags than the water did.
Then read it in the air, by its edge, with a phone you know works. If it reads normally, nothing is wrong and the tag was simply wet.
If it reads at contact only, the substrate has probably moved and the tag is degraded rather than recovered.
When water got inside
The signs are visible. Bubbling, curling, a cloudy patch under a laminate, an edge that has lifted, a paper tag that has gone soft.
There is no repair. A deformed antenna cannot be flattened back into tune, and a delaminated tag will keep taking on water.
Replace it, and treat the failure as information about the specification rather than as bad luck. A tag that lets water in is a tag chosen for the wrong environment.
Look at where the water entered. It is almost always an edge, which is the difference between a face laminate and a fully sealed tag.
What water never does
It does not erase the content. Data is stored electrically in the chip and water has no mechanism to change it.
It does not corrupt a message into something else. A tag either powers up and returns what it holds, or it does not power up.
It does not damage a chip that stayed dry inside a sealed body. A properly encapsulated tag can be submerged and keep working.
So a tag that reads and returns the wrong content has a different problem, and water is not part of it.
Frequently asked questions
Can a tag survive the washing machine?
A tag built for laundry can, and an ordinary sticker cannot. The wash is survivable and the finishing press is what destroys tags.
Should I dry a wet tag with a hairdryer?
No. Heat with trapped moisture delaminates the tag, which turns a recoverable situation into a permanent one.
Does rain stop a tag from reading?
It reduces the distance while the water is there and the tag usually still reads. Lasting failure means water got inside.
Can water erase my tag?
No. Data is stored electrically, so water has nothing to erase. A tag that returns wrong content has an unrelated problem.