You could call your local extension service to see if there is something up with that waterer. They might be able to test it? If it was something in the manufacturing, that should be figured out so others don't have the same problem. I would also report the problem to the feed store you bought it from and see if they have any other customers with the same problem. If so, perhaps there should be a recall on that lot.
When you get a new waterer, scrub it well and periodically disinfect it.
A large waterer should be OK for a couple days at a time, but I would have someone check on chickens at least every other day.
Also note that if you've indeed had botulism, it looks like it may exist on your property for sometime - so keep that in mind for any future chickens. I didn't research extensively, but this looks like it could be a concern.
When you get a new waterer, scrub it well and periodically disinfect it.
A large waterer should be OK for a couple days at a time, but I would have someone check on chickens at least every other day.
Also note that if you've indeed had botulism, it looks like it may exist on your property for sometime - so keep that in mind for any future chickens. I didn't research extensively, but this looks like it could be a concern.