Would you explain the Hadith: "Water is not made impure by anything"?

This hadith was narrated by Ahmad, Abu Dawud, An-Nasa’i, At-Tirmidhi, and Ibn Majah from Ibn Abbas, may Allah be pleased with both of them. Its purport is that water does not become impure by its use by a person in a state of major ritual impurity (junub), and it is a proof for the permissibility of purification with used water, and for the purity of a woman's leftover water. Another hadith narrated by Ahmad and Muslim from Ibn Abbas was used as evidence, stating that the Messenger of Allah, peace and blessings be upon him, would perform ghusl with the leftover water of Maymunah.

However, there is another hadith narrated by Abu Dawud and An-Nasa’i which prohibits a man from performing ghusl with a woman's leftover water or vice-versa, and directs them to scoop water together. Ibn Hajar reconciled these hadiths by interpreting the prohibition as one of discouragement (tanzih). In summary, it is permissible for spouses to perform ghusl from one vessel, with the preference being not to perform ghusl with the leftover water of one of them if the water is confined to it, though it remains permissible.