it does not become impure; for it remains in the state in which it was originally created, wholesome and covered by the Almighty’s words, “and He makes lawful for them what is wholesome.” The same legal reasoning applies to all liquids: if filth falls into them yet brings about no change in color, taste, or odor, they remain pure. End of citation.
The Council of Senior Scholars has issued a ruling on waters that have been polluted by impurities and then treated by technical means so that the impurity is removed. The decision reads as follows:
Decision No. 64, dated 25/10/1398 AH
After study, deliberation, and discussion, the Council resolved:
In light of the position of the jurists that a large quantity of water whose characteristics have been altered by impurity becomes pure again once that alteration disappears—whether it disappears on its own, by adding pure water, through lengthy stagnation, by the effect of sunlight, the passage of winds, or the like, for the ruling falls away when its cause falls away—
And since contaminated water can in fact be rid of its impurity by several means, and since purifying and cleansing it through modern technical methods of treatment is one of the finest means of purification—given the considerable material effort expended to remove impurities from such water, as attested and confirmed by highly qualified experts whose competence and experience are beyond doubt—
Therefore, the Council holds that the water is pure once it has undergone complete purification so that it returns to its original state and no change due to impurity can be detected in its taste, color, or smell.
It may be used to remove ritual states and physical impurities, and purification attained with it is valid.
It is likewise permissible to drink it, unless its use is proven to cause health harm; in that case it should be avoided to safeguard life and avert harm, not because it is impure.
While issuing this ruling, the Council nonetheless deems it preferable to dispense with using such water for drinking.