Sounds like your thermostat is stuck in the open position.
My understanding is that usually this will need replacing.
I'd just take it to a garage and hook it up to an electronic diagnostic tool to get a more definitive decision rather than advice from an online thread though! You could save yourself a few bucks and replace it yourself if it turns out to be the thermostat, however!
That has happened to me lots of times. Let it all dry out and it will probably be fine. I made a little water cover and put it over the front MFRU under the left front grate and it has not done it since.
I remember the first time this happened to me, I shut the car off, then turned the key on and the fan was blasting at full speed, sounded really weird. All was well after it dried out. I don't blast that area with water anymore.
I had an incident after washng. About 5 minutes into a 3 hour trip my front window fogged up and I had a mist of water blowing. Then I realized the fan had come on after warm up for the first time and blew the water from washing from between the radiator coils. Scared the crap out of me!