I also had the same issue. I washed my iphone 7 under water and after about half an hour the haptic engine stopped working. Now it works again. I remember i tried keeping the back of my phone close to my ear and i heard slight sparks. I left my phone shut down for approximately 5 hours. Then it worked for a while and stopped working again. After that i left it turned off overnight and then it started working and still is. I guess the trick is to make sure the water evaporates before it gets to do any permanent water damage.
I hope this helps.