To the best of my knowledge, chickens MUST have access to water whenever they have feed. If they don't have water that's not too cold or too hot, they can not digest their food. In cold weather, that can become pretty serious quickly. It looks like your set up worked well.

Regarding how much they should be eating, here's a spreadsheet from either a professor of poultry or a reputable feed mill owner, can't remember which sent it to me back in 2008: