You can replace home button if you are willing to give up touch ID, however it is possible that the button is dirty and/or was shorted by the contact with water, try cleaning it with a 90% isopropyl alcohol and a dry, soft cloth. another option is a third-party software you can use for you to try on fixing your unresponsive home button such as FoneDog iOS System Recovery. This may fix the issue.
Hope This Helps :)