Purity: Wudu with a Covered Wound When Water Is Not Harmful
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 328:
If it is not possible to uncover a wound but the wound and the thing that has been placed over it are pure, and if making water reach the wound is possible and not harmful, then one must make water go over the wound from top to bottom. If the wound or the thing that has been placed over it is impure, in the event that it is possible to wash that thing with water and make the water go over the wound, one must wash it with water and at the time of performing wuḍūʾ he must make the water reach the wound. In the event that water is not harmful for the person but washing it with water is not possible, or if uncovering the wound causes excessive difficulty or is harmful for him, he must perform tayammum.
-Ayatullah Sistani, Practical Laws of Islam, Purification (Taharah)