2000 Ford Taurus Steam from under the hood

I have noticed a few times in the past few months that there is a puff of steam that will occasionally come out from the front of my hood when I stop. I have been told that it is from going through puddle, but it has happened on dry days too. My coolant is sometimes low, but I do not see any fluid on the floor in the garage. What would the problem be, and should I be worried?