Is water considered impure if pigeon droppings fall into it without changing its characteristics, knowing the difficulty of cleaning the tank, and is it permissible to use this impure water?

The droppings of pigeons are considered pure by the majority of scholars, and they do not render water impure upon falling into it. If the water does not change due to their presence, it remains pure and sufficient for ablution (wudu’). This is based on the consensus of jurists that if something pure mixes with water and does not alter it, it does not prevent purification with that water, as the water remains in its absolute state.