the Permanent Committee of Saudi Arabia for Fatwâ and Research
This issue was under study by the Supreme Scholars Council of the Kingdom of Saudi Arabia. The following resolution was issued:
According to the report set by the experts in this regard, a large body of water would be deemed pure from any impurity if the impurity is removed, if more water is added to it, or if the impurity is eliminated by the passing of time, the sun, the wind, or any other cause that would remove it.
Impure water can be purified by the modern filtering techniques that are the best and most efficient methods of purification, in which many materials are added to remove impurities as attested to by experts in the field of water treatment.
Therefore, this Council believes that such water will be totally pure and it may be used for ritual purification and drinking as long as there are no negative consequences on people's health. If drinking is to be avoided, it is merely for reasons of public health and safety, not due to any ramifications of Islamic Law.
This Council recommends avoiding using this treated water for drinking purposes to avoid health problems and also in consideration of the negative public sentiment about this water.
May Allah guide us all, and may peace and blessing be upon our Prophet Muhammad.
Source: Islam Today