I use a rain barrel on the outside of the run. It’s large so it holds enough water to last weeks. I run two steel braided hoses out of it (one high and one low) into the run. I then installed a 4-5 ft long pvc pipe with fittings on each end that I attach the hoses to. On that pipe I installed 5 horizontal nipples. It’s gravity fed and keeps clean water available at all times. I don’t have to go in the run and can fill it once a month with a garden hose.
For winter I will put a stock tank heater on in the barrel and add a small pump to recirculate the water. It was quite easy to set up and I never have to worry about changing and cleaning water.
