Purity: Frequent Doubts During Wudu

Practical Laws of Islam as per the teachings of Ayatullah Sistani

Ruling 298:

Someone who frequently doubts about the acts of wuḍūʾ and its conditions – such as the water being pure and not being usurped – must not heed his doubts.

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