Is it permissible to perform Tayammum when water is cut off from homes and mosques, and if so, what is the Shafi'i school's evidence for the distance one must search for water (masāfat al-ghawth)?

The jurists agree on the condition of seeking water before performing tayammum unless one is certain of its absence, but they differ on the distance of this search. The Hanafis specified it as one mile, the Malikis as two miles, the Shafi'is as 400 cubits, while the Hanbalis considered it to be whatever is customarily close.

As for the Shafi'is, the traveler has four situations according to them: 1. If certain of the absence of water, he performs tayammum without searching. 2. If he presumes, thinks, or doubts the presence of water, he searches in his lodging and among his companions, and moves a distance equal to "Had al-Ghawth" (400 cubits). If he does not find water, he performs tayammum. 3. If he knows of water in a place a traveler reaches for his needs (beyond Had al-Ghawth), called "Had al-Qurb" (6000 cubits), he must seek it if he is safe for himself and his time. 4. If the water is farther than that (Had al-Bu'd), he performs tayammum, and is not obliged to seek the water due to its distance.

These limits are scholarly interpretations to ascertain the absence of water. The fundamental principle is to seek water based on Allah's saying: (And you find no water, then perform tayammum).

If water is cut off and there is great hardship in seeking it that is unbearable, tayammum is permissible. However, if the hardship is slight and bearable, seeking water is obligatory and tayammum is not permissible. The legal rule distinguishes between hardship that is usually inherent in worship and great hardship that necessitates alleviation.

Based on this, if bringing water from the fire station requires great and unusual hardship, tayammum is permissible. But if the hardship is usual, then bringing water for purification is obligatory.