Is it permissible for the school to fill its tank from the mosque's well without paying for tanker truck services, knowing that the well belongs to the school and is filled at the expense of the mosque or through the efforts of donors?

It is not permissible to use water purchased with the mosque's money, or donated by someone for the needs of worshippers in the mosque, for the school. Similarly, the pump endowed for pumping water to the mosque should not be used to pump water to the school. This is because dedicated water may not be transferred from its designated place unless it is known, or there is strong evidence, that its donor permits it.