Water is of three types: purifying water, which alone lifts ritual impurity, …
His statement, “Water is of three types: purifying water”: miyāh is the plural of water, and water is divided into three categories.
The first is purifying water (ṭahūr), with the first vowel pronounced as a, following the pattern faʿūl. This pattern denotes that by which something is done. Thus, ṭahūr refers to that with which one purifies oneself. Likewise, saḥūr, with the first vowel pronounced as a, refers to the food eaten before dawn.
As for ṭuhūr and suḥūr, with the first vowel pronounced as u, they refer to the act itself.
Purifying water is water that remains in its original state, either in reality—such that none of its qualities has changed—or by legal consideration, where it has changed through something that does not deprive it of its purifying quality.
For example, water drawn from a well while naturally warm, without having changed, remains as it is. Likewise, water that descends from the sky is purifying, because it remains in its original state. These are two examples of water that remains in its original state in reality. By our saying, “or by legal consideration,” we mean such as water changed by something that does not mix with it, or water changed by something from which it is difficult to protect water. Such water is purifying, although it has not remained in its original state in reality. The same applies to heated water: it is not in its original state, because it has been heated; nevertheless, it is purifying, because it is deemed to remain in its original state.
His statement, “which alone lifts ritual impurity,” means that nothing lifts ritual impurity except purifying water.
Thus, gasoline and the like do not lift ritual impurity. Nothing besides water lifts ritual impurity. The evidence is Allah’s saying: “But if you do not find water, then perform dry ablution” [al-Mā’idah 5:6]. He commanded that one resort to dry ablution when water is unavailable, even if other liquids and fluids are available.
According to the established position of the school, the earth used in dry ablution does not lift ritual impurity.