水(みず)が美味しい(おいしい)お酒(さけ)だったから父親(ちちおや)に飲ませ(のませ)たくて

When Kosuke scooped up the water from the waterfall and drank it, to his surprise, it tasted like delicious sake! 'Father will surely be pleased!' Kosuke put the sake into his gourd and hurried home.