I say, and with God's success: It is disliked to exceed the customary amount of water used for ablution. Anas  said: "The Prophet  used to perform ablution with a mud (a measure of water), and he would bathe with a sa' (a measure) up to five mudds." (Sahih Muslim 1/257, and Sahih Bukhari 1/84, and Sunan al-Tirmidhi 1/83, and al-Tirmidhi said: This is a good and authentic hadith. The mudds are the plural of mudd, which is a quarter of a sa', meaning that his washing would reach up to five mudds. According to Abu Hanifa and Muhammad, a sa' is eight ratls (a weight measure) in Baghdad. According to Abu Yusuf, it is five ratls and a third. Ibn Umar  said: "The Messenger of Allah  saw a man performing ablution and said: Do not waste water, do not waste water." In Sunan Ibn Majah, 1: 147, and from Abdullah ibn Amr : "The Prophet  passed by Sa'd while he was performing ablution and said: What is this wastefulness, O Sa'd? He said: Is there wastefulness in ablution? He said: Yes, even if you are by a flowing river," in Musnad Ahmad 2: 221. Sheikh Shu'ayb said: Its chain of narration is weak, and he said in Al-Hadiyah Al-Ala'iyah, p. 26: "It is disliked as a matter of preference if it is flowing and he does not believe it is a Sunnah, but if he believes it is a Sunnah, it is prohibited. As for the water used for purification from a cistern, pool, or pitcher, it is forbidden." See: Tabyin al-Haqaiq 1: 7, and Al-Hadiyah Al-Ala'iyah, p. 26, and Allah knows best.