Al-Qamar 54:28

Wanabbi/hum anna almaa qismatunbaynahum kullu shirbin muhtadar

And inform them that the water is shared between them, each [day of] drink attended [by turn].

and tell them that water (of the well) is to be shared between them (and the she-camel), so as the right of having water shall be attended by each (alternatively).