Kawarayu is a free-flowing onsen, which is extraordinarily rare. Although normally onsen are filled with spring water that is piped in from elsewhere, this bath is built on top of a depression in the bedrock where the water from higher up the mountain flows down and gathers naturally. Open slats in the sides and bottom of the basin allow the spring waters to flow freely through the bath.
Like the Kamiyu and Shimoyu baths, the water temperature at Kawarayu bath fluctuates but can reach temperatures of up to 50° C. Visitors should enter the bath slowly to give themselves time to adjust to the heat, and once submerged, hold still to let their muscles fully relax. Bathers should refrain from splashing and supervise their children. There is no specific rule regarding the age at which children can enter the hot springs, but there is a risk of heatstroke for any child younger than four years old.