I always think about iamcuriositycat's experience - a garden hose used to supply water was leaching a chemical that prevented her flock from laying.
I would think about switching out watering buckets - especially if they are plastic (try stainless steel - used ones are not that hard to come by around here). Try a different hose if you use one for their swim water.
What feed are you using? How often do you feed, and how much? Any supplements? Free choice oyster shell on the side? What's their environment like? Noises? Other animals?