Is it permissible to use the public water supply for washing cars?

Question

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)

Conclusion:

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.

Please see also the answer to question no.
70274 and 72384

And Allah knows best.