[der Geist]

Sound like everyone here has great advice for you. It should be easy to pinpoint the exact location of the leak. It must be inside your engine compartment since steam is venting. Fill up the resivoir, let it sit for a while (the longer the better) and see if there are any apparent leaks dripping. If not open the engine cover and start the car letting it idle to operating temp. You should keep an eye on your resivoir just in case it is leaking from the bottom where you can't see it. With the top up it should be relatively easy to see where the leak is by following the steam back. It may be a something simple you can reair yourself.