Is the water used for istinja' while standing, employing the hand and pouring a lot of it on the area, considered absolute, purifying water, despite doubt as to whether it reached all places?

The water used to remove impurity must be pure [tahur]. Performing istinja' while standing does not deprive the water of its purity. What is obligatory for a woman in istinja' is to wash what becomes visible when she sits to relieve herself, which is only the outer part of the private organ. A strong presumption of cleanliness is sufficient for removing impurity.