The Prophet ﷺ passed by Saʿd as he made wuḍūʾ and said: “What is this extravagance?” Saʿd asked: “Is there extravagance even in wuḍūʾ?” He ﷺ said: “Yes, even if you are on a flowing river.” (Aḥmad & Ibn Mājah — ḥasan). He ﷺ himself would make wuḍūʾ with about a mudd (a handful) of water. (al-Bukhārī).
العربية: عن عبد الله بن عمرو رضي الله عنهما أنّ رسول الله ﷺ مرّ بسعدٍ وهو يتوضأ فقال: «ما هذا السَّرف؟» فقال: أفي الوضوء إسراف؟ قال: «نعم، وإن كنتَ على نهرٍ جارٍ». (أحمد وابن ماجه).
Turn the tap low during wuḍūʾ — saving water is itself a Sunnah.