Without electricity you may have to carry water out there a couple of times a day so they can drink before it freezes during the colder parts of the winter.
How far is the coop from your house? I run a 100ft extension cord from an outlet on the outside wall of my house to the chicken run. The outlet has a weatherproof cover that closes around the cord and the cord is an outdoor rated cord. I have a 55 gallon plastic food grade drum with water and I bought a stock tank heater that was made specifically for plastic containers. It doesn't get hot enough to melt plastic and has a built in thermometer so it only heats up when it needs to. The whole thing gets submerged in the tank and keeps the water thawed all winter. Where the heater plugs into the extension cord, I bought a weather proof cover that closes around the ends of the mated plugs to keep them dry. Worked that for 3 years now with no issues.
Seems like keeping their water from freezing and keeping their poo from building up too much is 99% of the work that goes into caring for chickens.