I stayed in a place that's indoor plumbing was a variation of this idea. The entire house was solar and but didn't store
energy well. The cabin had been vacant for a few years and the batteries were not maintained. There was a 55 gal water tank on the second story and a small pump that ran the spring fed water to the tank. The water was then gravity fed through the house. The water also ran through on of the
wood stoves and was stored in a smaller hot water tank. This was in Vermont and I was there over the winter solstice. We had to monitor and maximize our energy use because there wasn't much sunlight. So during sunny days we ran the pump and on cloudy days we hoped for sunny days.