Not being wasteful with water
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Etiquette of Purification (Wudu & Ghusl)
Not being wasteful with water
"O children of Adam, take your adornment at every masjid, and eat and drink, but be not excessive. Indeed, He likes not those who commit excess."
Reference: Qur'an, Surah Al-A'raf 7:31 (Note: the popularly cited hadith of Sa'd and the flowing river, Sunan Ibn Majah 425, is graded Da'if [weak] by Ibn Hajar and most later scholars, so it is not relied upon here.)
Explanation
This general Qur'anic principle against excess is applied by scholars to water usage in wudu, cautioning against extravagance even where water is plentiful.