Don't contact the manufacturer yet claiming it's a manufacturing defect or trying to hide what happened - they'll either see water damage indicators inside the device or catch the inconsistency in your story, and that'll tank your claim instantly. Accidental water damage is almost always excluded from standard manufacturer warranties, even if your watch is technically water-resistant. There's a huge difference between being water-resistant (meaning it can handle splashes or brief submersion) and having accidental damage coverage. Most warranties specifically carve out damage from accidents, spills, or misuse, treating those as your responsibility rather than a product defect.
Your best move is to check your watch's actual rating first. If it's rated IP67 or higher, splash damage from dishwashing might legitimately fall within its designed use - in that case, the manufacturer could potentially cover it as a defect in water sealing rather than "accidental damage." Look at your warranty document or the manufacturer's site to see exactly what they exclude. Some companies are more lenient about this than others, and a few do cover limited water damage if the device was used as intended.
If the warranty truly excludes accidental damage, your real options are either paying out of pocket for repair or checking whether your homeowner's/renter's insurance or credit card purchase protection covers accidental electronics damage. Some cards do cover this within the first few months. It's worth a shot before giving up on the watch entirely.