MUBTILAATE - WUDHOO (Things Which Invalidate Wudhoo)
Wudhoo becomes batil on account of the following things:

1. Passing of Urine.
2. Excretion.
3. Passing wind.
4. A sleep, deep enough to restrict both sight and hearing. However, if you can hear the sounds around you, wudhoo does not become batil.
5. Things on account of which a person loses his sensibility, like insanity, intoxication or unconsciousness.

WAJIBAATE - WUDHOO (When Wudhoo Is Obligatory)

1. For all Wajib (Obligatory) prayers. As regards Mustahab prayers, wudhoo is a condition for their validity except for Salaat-ul-Mayyit.
2. When touching the writings of the Holy Qur'an.
3. For the obligatory tawaf of Holy Ka'abah.
4. It is better not to touch the names of our Ma'soomeen (a.s.) without first performing wudhoo. If this is done with the intention of showing disrespect, then the act will be considered haraam.

A Holy Verse
About wudhoo, the Qur'an says in one place:
"O you who believe! When you rise up to prayer, wash your faces and your hands as far as the elbows, and wipe your heads and your feet to the ankles; and if you are under an obligation to perform a total ablution (Ghusl), then wash yourselves…"
Sura Maidah, Verse 6

THINGS TO REMEMBER…

1. The water for wudhoo must be pure and not mudhaaf (mixed) like rose-water or water mixed with clay that changes its colour. In such a case, the water cannot be recognised as pure and wudhoo will be considered batil.

2. The container of the water used must also be clean and pure. If it (the container) is ghasbi, then the wudhoo will be batil.

3. The place where wudhoo is performed must be clean. If it is utilized without the permission of its owner then such an act is haraam and wudhoo performed there will be nullified.

4. At the time of performing wudhoo, all the parts used in doing wudhoo must also be taahir i.e. face, hands and legs. If the parts not directly used in wudhoo are najis, then the wudhoo is still considered correct and valid.

5. A person must perform wudhoo by himself. If someone else assists him in washing his face, hands or wiping of feet, then the wudhoo will be considered baatil.
   
   Special Circumstances:
   
   If a person is unable to perform wudhoo, he can ask assistance from another. However, he must make his niyyat (intention) himself. He should attempt to perform those parts of wudhoo that he can by himself and seek assistance for those he cannot.

6. If, by performing wudhoo the health of a person can be harmed, then he should perform tayyamum instead.

7. If a person does not have enough time to perform his wudhoo and pray before qadha then he is allowed to perform tayyamum instead. However, if the time he takes for wudhoo and tayyamum is the same then he should opt for wudhoo.