Is the ablution of one who follows the opinion that "ablution water remains valid for ablution unless its color, taste, or smell changes" considered sound, given the presence of impurity on the hand, without definitively asserting that the water has changed due to it, or attempting to confirm such a change, whether this occurs in normal circumstances, for someone with obsessive doubts, or for someone experiencing hardship?

The cure for obsessive thoughts is to disregard them and pay them no mind. If someone performs ablution (wudu') or a ritual bath (ghusl) and there is impurity on one of their limbs that does not prevent water from reaching the skin, then their purification is valid, and their ritual impurity is removed. A person afflicted with obsessive thoughts should adopt the more lenient opinions of the jurists. The water that separates after washing an impure limb has a specific ruling. The fundamental principle is that water remains pure and does not change; therefore, if someone doubts the impurity of water, there is no harm in performing ablution with it, because the default state is its purity.