Purity: Ruling on Non-Spring Flowing Water Less Than Kurr

Practical Laws of Islam as per the teachings of Ayatullah Sistani

Ruling 34

With regard to water that flows on the earth but does not gush from it, in the event that it is less than kurr and an impurity comes into contact with it, it becomes impure. However, if the water flows from above and an impurity reaches its lower part, its upper part does not become impure.

-Ayatullah Sistani, Practical Laws of Islam, Purification (Taharah)