Does running water (Al-Ma' al-Jari) become impure except through physical change?

Primary text

Impurity does not affect flowing water (Al-Ma' al-Jari) unless a change in its properties occurs. This is deduced from the ruling that Hammam water, which is considered analogous to flowing water because the older water is pushed out by the newer, is deemed pure. If flowing water were rendered impure without change, the characteristic of it being 'flowing' would have no legal effect regarding purity.