Senjyu no Yu is located only a few minutes from Hatsushiba station. While they don't have a spring on the premises, they do tank spring water in from Kameyama city in Mie prefecture twice a week according to one website. Of course being a tanked in onsen that means the water is recycled and treated rather than being a constant fresh stream. I went here 5 years ago and remember it being a good basic supersento. One unique addition was the blow dry room which only kind of worked.