Since a new key is cheap and you can program it yourself if you have two working keys, I recommend getting a third now in case your washed key decides to quit working. If you only have one working key you have to have a dealer/locksmith program a new one.
As a plumber, I use these blue pills that contain a very potent dye. It dissolves in the water and you can trace it. Unfortunately I left 1 in my pocket and the wife did our shared laundry.
Her delicate unmetionables turned bright blue. My trousers already blue grew larger and a bit stiff
Ok sorry, forgot to check. Won't do that again. 2 weeks later, whoops I did it again.
Now I do my own laundry and stopped using the blue pills. I use food coloring instead. Green and blue are my go too Red and yellow, not so much except for Halloween and April 1st. In the toilet tanks.
I've heard from friends about dropping keyfobs from docks into ocean water, then having them recovered (by whoever is around with a wetsuit and mask) to find they still work.
I hereby do not volunteer to test this with my third fob (having done what @RocketGhost recommends) but someone, perhaps I, will no doubt do the test accidentally sometime.