It was an amber liquid, but when it's watered down it becomes a cloudy, white drink.
It was an amber liquid, but when it's cut with water, it becomes a cloudy, white drink.
ご質問ありがとうございます。
「琥珀」はamberと言います。英語ではamberは「琥珀」と「琥珀の色」の意味を持っています。
「水で薄める」はto water downとかto cut with waterとかto weaken with waterなどに訳せます。
例文:When it is weakened with water, it becomes a cloudy, white drink.
ご参考いただければ幸いです。