My Mum had just purchased a Le Creuset Casserole with enamel coating and is wondering how you add liquid to it when it is already hot without cracking the enamel? This not only includes water, but wine and beer as well.
Adding cold liquids to a hot enameled pan is not going to crack the enamel, you can add a cold beer to a dish without worrying about your cookware. The main thing to keep in mind when adding cold liquids is that it will bring the temperature down below your desired cooking temperature, you will need to either crank up the heat to bring it back up to the desired temperature quickly or lengthen the overall cooking time.
Don't worry about it. I have poured white wine or other liquids straight from the refrigerator into a hot Le Creuset casserole, in order to deglaze drippings and make a pan sauce, more times than I can count. I can't speak for cheaper enameled pans, but Le Creuset cookware is made to take this kind of treatment.
You won't damage the enamel in any kind of normal cooking scenario--you would have to deliberately try very hard to scratch it with a stiff, sharp metal utensil like a chef's knife, or heat the casserole for an extended period of time with nothing in it, which could possibly cause crazing of the enamel. (If you want to preheat the pan before adding food, add some oil or other liquid while it heats up first.)