What is the ruling on turning on the water for an unveiling sister so she can get ready to go out?

If the sister's going out immodestly (mutabarrijah) depends on her using water, which is only possible by turning on the water pump, then it is not permissible to turn it on, because it is an aid to sin. This is based on the Almighty's saying: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression." However, if her going out does not depend on that, then there is no harm in turning it on. And it is obligatory to advise the sister to abandon immodest display (tabarruj) and to explain its prohibition.