Unterwasser is a village in the Toggenburg region of the canton of St. Gallen, Switzerland, situated at the confluence of the two streams forming the upper Thur. Formerly part of Wildhaus municipality, it has since 2010 been part of Wildhaus-Alt St. Johann by merger of Wildhaus and Alt St. Johann. It is a relatively small ski resort, and many of its trails are shared with nearby Wildhaus.
