Is it sufficient for purification (istinja') to turn on the water once or twice, or is it necessary to ensure the complete removal of urine, especially given the presence of hair in the area, to avoid obsessive doubt (waswasa) in prayer?

It is sufficient in istinja' (washing after defecation or urination) with water to pour it over the impure area and let it flow until it is highly probable that the impurity has been removed, whether there is hair or not. There is no specific number of washes required. Some jurists, however, consider it commendable to wash three times when performing istinja' with water. As for women, they must wash what becomes visible from their private parts when they squat to relieve themselves; they are not required to wash what is concealed.