井泉[seisen] (water) well
黄泉[kousen] underground spring
温泉[onsen] spa
九泉[kyuusen] hades
源泉[gensen] source

古泉学[kosengaku] numismatics
鉱泉[kousen] mineral spring
泉貨紙[senkashi] reclaimed paper
泉水[sensui] fountain