i kept marbles in my chicks waterer until they were about two weeks old. i use one of those plastic things, with the container that screws into a shallow dish, the kind you get at the feed store.
For the first two weeks I used the type of waterer that airheart43 described; a plastic quart reservoir with a screw-on plastic basin. I didn't use marbles, although it's recommended that you do. After that my chicks graduated to the 3 gallon waterer that I still use today and boy! do I love this waterer; filling once a day instead of multiple times. All in all, I'd say two weeks of marbles.