Is there a puddle of water under the waterer? (More than little splashes or drips that would be expected)
If not, then just continue giving the chickens as much water as they need (they aren't going to drink more tax what the weather, health, growth, etc calls for).
oh- looks like I misunderstood: you are concerned they aren't drinking enough rather than too much. Of course. Could be they don't like the nipples. I have two nipple, one double wall metal, and a variety of dish/bowls full of water out at any given time. The dishes stay out (in the run), and fill with rain water or get filled. In the coop and covered run are the nipples and metal waterer. No question the dishes are favored, then the traditional metal waterer, and only if those are empty do they bother with the nipples. Trying to change that, as the nipples are so much cleaner, easier, and less wasteful. I think - hope - that eventually they will drink from whatever source, even if it means letting them get a bit thirsty during the transition.