Are surfaces touched by a father's hand, contaminated with sewage water, considered ritually impure (najis) by abstract impurity (najāsa ḥukmiyya) that has no color or smell?

Obsessive thoughts must be cured by ignoring them. The water that touched your father is pure unless it has been altered by impurity. The default state of things is purity until their impurity is definitively proven with certainty. If a ritual impurity is confirmed, it is sufficient to pour water over its location to purify it. The default rule is that impurity does not transfer through doubt.