Are the waters that collected in the bathtub as a result of istinja' (washing after defecation/urination) considered impure and would they cause the house to become defiled if a person stepped on them with their feet?

We fear that the questioner may be afflicted with waswas (obsessive doubts) regarding purification, and we advise her to close the door to such doubts. The water collected in the basin does not become impure from the water used for istinja' (washing after relieving oneself) if it separates without changing [its characteristics]; because the wash-water from an impure substance, if it separates without changing [its characteristics], is considered pure, as stated in Imam Al-Nawawi's Minhaj: "The more apparent opinion is the purity of wash-water that separates without change, after the place has become pure." Therefore, her feet are pure.