What is the ruling when a thirsty person finds both pure and impure water, sufficient for drinking?
Chapter on Tayammum
Al-Mughni
Book of Purification
Primary text
If a person fearing thirst finds pure water and impure water, and one quantity suffices for drinking, the pure water must be reserved for drinking, and the impure water may be poured away if drinking is not necessary. The justification is that the person cannot secure water permissible for ablution or permissible for drinking except through this pure water. Therefore, reserving it when fearing thirst is permissible, analogous to the situation where only this water exists.
Supporting text
The Qadi stated that ablution must be performed with the pure water, and the impure water reserved for drinking, based on the premise that the pure water is available and need not be used for drinking. Some Shafi'is held that if the time for prayer has arrived, the impure water should be drunk because the pure water is reserved for ritual purity and is thus treated as non-existent. This view is rejected because drinking impure water is forbidden, and the pure water only becomes exclusively reserved for ritual purity after the need for drinking is negated, which is not the case here, as the presence of impure water is effectively like its absence due to its prohibition for consumption.