When I use to live in Sanda, Kanoko was the closest onsen to my apartment. It would take me 15 minutes or so to ride there on my bike, so I'd often go there before or after work. I went here 2 or 3 times a month. I do miss riding my bike here through the rice fields to enjoy this wonderful place.
The sento is different on each side, but both have the same basic layout. The bath on the left side of the front desk has a nicer rotenburo and a salt sauna. The bath on the left, my favorite, has a very strong jet bath and a extra hot sauna. Although small, Kanoko offers well designed baths that get better the more you go. Heated spring water fills the baths here. It's not the best onsen, but it feels extra hot and is also is mildly radioactive.
I go here for the baths, atmosphere, and the super hot sauna--not the water so much. As a daily onsen, Kanoko doesn't get boring. Kanoko has free body soap and shampoo, and a very good point card system with many discounted or double point nights to take advantage of. For a while there I rarely paid the full ¥600 price. Kanoko Onsen has a sister sento, Karato Onsen, which is one of my wife's favorite spas and has a very similar feel, but much bigger.
March 2020 Update: First time back here in awhile. I am not sure if Kanoko is still using well water in the baths or not. There were not any signs that I saw with the spring quality information, but I was not really looking for them. I was in the dry sauna (right) side this time and forgot how much I enjoyed this place. The cold water bath here is lovely after the really hot sauna they have. We saw a fox in the fields next to the parking lot when we drove in also. Such great luck!