Praise be to Allah.
The Messenger (blessings and peace of Allah be upon him) said: “The Muslims are partners in three things: herbage, water and fire.”
Narrated by Abu Dawood (3477); classed as saheeh by al-Albaani in Saheeh Abi Dawood.
And he (blessings and peace of Allah be upon him) said: “There should be neither harming nor reciprocating harm.”
Narrated by Ibn Maajah (2340); classed as saheeh by al-Albaani in Saheeh Ibn Maajah.
The water referred to in this hadith is ordinary water that is not under the control of anyone, such as seas, rivers and so on.
Al-Kashmiri (may Allah have mercy on him) said in al-‘Urf ash-Shadhi (3/84):
There are three categories of water:
1. Water for which no one has undertaken any work in producing it, such as naturally occurring rivers. In this case it is permissible for anyone to set up a water wheel.
2. Where a group of people dig a small stream. In this case it is permissible to give animals water from it, but it is not permissible to irrigate land from it or to set up a water wheel.
3. Water that is stored in vessels. It is permissible to drink from it and it is permissible to take it by force in the case of necessity. End quote.
It says in al-Mawsoo‘ah al-Fiqhiyyah (25/376):
With regard to water that is stored in vessels and the like, it is the property of the one who placed it in the vessel, according to the consensus of the fuqaha’, and no one has any right to it, because even though water is permissible (to everyone) in principle, that which is permissible (to everyone) may become the property of a particular individual if he seizes it, if it is not the property of anyone else, as in the case of firewood, herbage and game (wild animals that are hunted), and it is permissible to sell it, give it as a gift and give it in charity.
The custom in all Muslim lands, and in all historical periods, has been for providers of water to sell water stored in vessels, without anyone objecting to that, so it is not permissible for anyone to take it without the permission of the one who put it in the vessels, except in the case of one who fears that he may die; if someone else has water surplus to his needs, then it is obligatory for him to give it to him, and if he refuses to give it to him, then (the one who is dying of thirst) may fight him for it. End quote.
See also: al-Mawsoo‘ah al-Fiqhiyyah (1/79-80); al-Fiqh al-Islami wa Adillatuhu (4/419-420)
With regard to public water that is prepared by the state to meet specific needs of the people, such as drinking water and the like, this type is more like water that is provided for charitable purposes, i.e., as a waqf (endowment). Therefore attention should be paid to the specific purpose for which it was allocated, and it should not be used for any other purpose, except in cases where it is usually used for another purpose without any objection, or if one uses only a little, such as is usually overlooked.
Shaykh Mustafa ar-Ruhaybaani (may Allah have mercy on him) said:
With regard to water that is provided for drinking as an act of charity, it is not permissible to use it for wudoo’ or ghusl, or for cleaning impurities from the body, or any other purpose.
End quote from Mataalib Ooli an-Nuha (1/104)
He also said:
The one who enters the hammam (public baths) should be careful in his use of the water, using only as much as he needs to, because it is privately owned or provided as an act of charity or waqf. Using only what is needed is what is allowed according to sharee‘ah and custom, as is known from traditional practice, especially hot water, because of the effort involved in acquiring it by obtaining fuel and giving wages to workers. A similar case is that of water that is given in charity for the purpose of wudoo’, or ghusl in the case of janaabah (major impurity following sexual activity) or following the cessation of menses or postpartum bleeding (nifaas), or for the removal of impurity: no more should be used than is necessary.
End quote from Mataalib Ooli an-Nuha (1/189)
Shaykh Muhammad ibn ‘Umar al-Jaawi ash-Shaafa‘i (may Allah have mercy on him) said:
If there is nothing available except water that has been given in charity or as a waqf to be used for purposes other than purification, if it is known that the donor intended people to use it in whatever way is beneficial for them, then he may use it for the purpose of purification, and it is not permissible for him to do tayammum. If he is not sure about that, then he may refer to custom and other indications, and it is not permissible for him to transfer water that was provided for drinking as an act of charity from its place to another place, such as taking it to drink in his house, for example, unless it is known or there is an indication that the donor would allow that.
End quote from Nihaayat az-Zayn (p. 36)
With regard to carrying water in a vessel to serve a need, what appears to be the case is that it is something that is usually overlooked, especially if there is a need similar to that for which the water was given in charity to serve that need and was placed in that public place, or if it is for a need that is more serious than that.
With regard to washing cars, it appears that whoever provided the water in that place would not allow that, especially as there is obvious harm that results from washing cars in places other than those that are specifically set aside for that purpose.
If those who are in charge of that place allow that, or if custom allows that without any objection, and no obvious harm results from that, then there is nothing wrong with it, in sha Allah.
And Allah knows best.