This article is from the Care of Orphaned Kittens FAQ, posted to rec.pets.cats newsgroup. Maintained by Sharon Talbert with numerous contributions by others.
By four or five weeks, the kitten should be taking water on its own as well as food. Provide a low, heavy dish, so the kitten can walk in it, dip its paws and otherwise perform the scientific experiments typical of all felines. If you can, place the dish in a corner or other low-traffic area and handy but not too close to the food dish. You may need to help the kitten by providing it with an opaque rather than a clear dish and by wetting its nose with your finger and leading it down to water level. Given the kitten has been lapping up its moosh-meals for a while by now, drinking water shouldn't be too great an adjustment.