Once back in Agata Forest, locate Kokari and speak with him. He will tell you that his dog has disappeared. It will be a while before you find Ume. For now, head north along an upward-sloping path to reach the Hitoshio Spring and speak with Kushi who should be standing by. Speak with Kushi a few times and the camera should swing upwards, highlighting the spring and the open barrel next to it. Using the Waterspout brush technique, fill the bucket of water to trigger a cutscene during which you need to help Susano fight off some troublesome Imps.