What is its reality? What are its categories?
"Purification" is the removal of an impediment affecting all the limbs, which is the major purification called ghusl, or only affecting some of the limbs, which is the minor purification called wudu'.
What is meant by an 'impediment' is a state which does not allow a man to perform his worship, such as, for instance, his state when one of the things which breaks wudu' (such as urinating) overcomes him and prevents him from performing the prayer.
There are two categories of purification:
1) Purification from ritual impurity.
2) Purification from actual filth.
What is hadath (ritual impurity)? How many categories does it have?
It is an impediment affecting all the limbs, which is the major impurity and obliges ghusl, or an impediment affecting some of the limbs, which is lesser impurity and obliges wudu'.
What is the purification of filth? What is used for it?
It is the removal of impurity from the garment, body and place of someone who prays. It can be done with any type of water since what is under consideration is the removal of the impurity itself and cleaning of its location.
Are there different categories of purification from ritual impurity? What is used to achieve it?
There are two types of purification:
1) that done with water, which is wudu' and ghusl
2) that done with earth, which is tayammum.
Only pure water may be used.
What is pure water?
It has two preconditions:
1. That it remains on its basic nature in that nothing is mixed with it, such as sea water, well water, water collected from dew and water which has melted after having been frozen and ice.
2. That neither its color or smell or taste has been altered by something which is normally separate from it, whether that substance be pure or impure.
21. What is the ruling on changed water?
1) Water which has been changed by the addition of an impurity, such as blood, corpses or wine. This type of changed water may not be used for general use or for worship.
2) Water which has been changed by the addition of something pure which is separate from it, such as milk, ghee and honey. This type of water may be used for general use (such as cooking) but not for worship.
3) Water which has been altered by something pure that is inseparable from it, like red clay, salt, Sulfur and earth, or has been altered by that which falls or is thrown into it but is part of the earth around it, such as dry mud, even if it is thrown in intentionally. This type of water may be used for both worship and everyday uses. This ruling is also true for water whose state is altered by stagnation or by fish and moss growing and living in it, or by the leaves of surrounding trees falling into it, as this is impossible to avoid.
What water is it disliked to use for purification?
It is disliked to use a small amount of water for wudu' or ghusl if that water has already been used to perform one of them, just as it is disliked to use water into which impurity has fallen, which is not sufficient to change its state, even if this water were only to be used for the purification of actual filth (khabath). It is also disliked to use water which has been lapped by a dog.