A "spring source" is hot spring water that gushes out from the surface of the earth. There are three ways that hot spring water gushes out: "natural spring water or artesian water", where hot spring water gushes out naturally from the surface of the earth; "mined artesian water", where hot spring water is dug up by drilling and water pressure is applied to gush out; and "drilling powered pumping", where hot spring water is dug up and pumped up with a pump. Representative five-star inns include " Nisshinkan " in Manza Onsen , Gunma Prefecture, and " Yuyado Unzen Shinyu " in Unzen Onsen , which are artesian hot springs. The hot spring water gushes out without the use of any power source.

"Free-flowing from the source" means that the raw spring water, without any added water or heating, is allowed to overflow into the bathtub, and the overflowing water is not reused. For example, the selling point of "Unzen Fukudaya" in Unzen Onsen , Nagasaki Prefecture, is its milky sulfur spring, 100% free-flowing from the source. It also contains a lot of metasilicic acid, and the clear, cloudy water will help you regain your energy. At " Hizenya " in Tsuetate Onsen , Kumamoto Prefecture, you can enjoy 100% free-flowing from the source in Kissho-no-Yu, which has five baths for men and women.

In the general understanding, the concept of free-flowing hot spring water includes adding water to the source to the extent that the composition of the spring water is not changed, and heating a low-temperature spring water to a temperature suitable for bathing. As this is certified under the Hot Springs Act, it can also be considered a genuine hot spring. When the source is shared by an entire hot spring resort, it is not rare for water to be added at the source and supplied to each lodging. Some lodgings also make an effort to allow guests to enjoy the hot spring water to the fullest by adding fresh water that springs up on the premises, rather than tap water. One example is Miorine no Yado Sansuiso in Tsuchiyu Onsen, Fukushima Prefecture.

In many inns, even if spring water is poured into the large public bath or open-air bath, the water can become dirty or dirt can accumulate in the bathtub when many people bathe in it, so as a hygiene measure they are forced to recycle, filter, sanitize, and reuse the water. This is why even inns with excellent hot spring quality cannot make a big deal about their hot spring water being free-flowing from the source. In many cases, such inns provide free-flowing hot spring water in private open-air baths or in some of the guest rooms.

In contrast, 100% natural spring water means that no adjustments are made to the spring water. It is a pure spring water that is not diluted or heated, and does not undergo chlorine disinfection through circulating filtration. At Atami OnsenFuruya Ryokan , Shizuoka Prefecture, the source spring water "Kiyozaemon no Yu," which is known for its skin-beautifying properties, flows freely through separate piping in the baths of all rooms in the entire building.