They can be used with a rain barrel, I chose the bucket because in the winter I put a stock tank heater in with a long run using a barrel it would freeze solid not sure where you live and even have to worry about freezing, I have never tried the cups again for freezing reasons, my girls were around 10 months when I switched them over and they were using them with in 2 minutes just tap them and they see the silver nipple and start pecking at it,you need a tiny hole in the top of the bucket so it doesn't form a vacuum, I got them from"all bout chickens".