Purity: Conditions for the Validity of Wudu
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Conditions:
There are a number of conditions for wuḍūʾ to be valid.
The first condition: the water used for wuḍūʾ must be pure, and based on obligatory precaution, it must not be tainted with anything that human beings find disgusting – such as the urine of an animal whose meat is lawful to eat, a carcass that is pure, or pus from an injury – even if it is pure in Islamic law.
The second condition: the water must not be mixed.
The third condition: the water must be permissible (mubāḥ) to use [i.e. it must not be usurped].
The fourth condition: the parts of the body on which wuḍūʾ is performed must be pure at the time of washing and wiping, even if one purifies them during wuḍūʾ before he washes or wipes.[47] If the washing during wuḍūʾ is performed with kurr water or suchlike, then purifying an impure part before washing is not necessary [as it will become pure during the wuḍūʾ].
The fifth condition: there must be sufficient time for performing wuḍūʾ and prayers.
The sixth condition: one must perform wuḍūʾ with the intention of attaining proximity to Allah the Exalted, and it is sufficient to perform it with the intention of following the command of Allah the Exalted. If one performs wuḍūʾ to cool down or with some other intention, it is invalid.
The seventh condition: wuḍūʾ must be performed in the sequence (tartīb) mentioned earlier, i.e. first the face must be washed, then the right arm, and then the left arm; following that, the head must be wiped and then the feet. And based on obligatory precaution, one must wipe the left foot after the right foot.
The eighth condition: the acts of wuḍūʾ must be performed in close succession (muwālāh).
The ninth condition: washing the face and arms and wiping the head and feet must be performed by the person himself; if someone else performs wuḍūʾ on him or helps him in getting the water to his face and arms, or in wiping his head and feet, his wuḍūʾ is invalid.
The tenth condition: using the water must not be harmful for the person.
The eleventh condition: there must not be an obstruction for water to reach the parts of the body on which wuḍūʾ is performed.
-Ayatullah Sistani, Practical Laws of Islam, Purification (Taharah)