Water that is used to wash clean clothes, utensils and other pure items can be used for wudhu and ghusl as long as its density does not change and as long as it is still referred to as water in normal conversation. But if there was some food or drink in the utensils, then using that water for wudhu or ghusl will only be permissible if at least two of the three qualities of water remain unchanged. If two qualities change, wudhu or ghusl will not be permissible.
It is makruh to drink used water, or to use it in cooking. wudhu and ghusl with such water is not permissible. However, it can be used to wash impurities.
The one who is in need of wudhu should not make wudhu with zam zam water. Nor should it be used by the one who has to have a bath. To wash impurities with it and to make istinja with it is makruh.
However, if one is compelled to use it, in the sense that water cannot be found within 1.6 kilometres, and one cannot purify one’s self in any other way, then all these things will be permissible with zam zam water.
The water that is left behind by a woman after she made wudhu or ghusl should not be used by a man to make his wudhu or ghusl. Although this is permissible according to the Hanafi Mazhab, it is not permissible according to Imam Ahmad (Hanbali Mazhab). It is therefore better to abstain from those matters in which there is difference of opinion.