Is it obligatory to purchase water if its price is equal to its market value or slightly higher, provided the person can afford it?
Chapter on Tayammum
Al-Mughni
Book of Purification
Primary text
It is obligatory to purchase water if it is being sold at its usual market price in that location, or at a small increase in price, provided the person can afford it and has no pressing need for that money, considering the necessity of water and the expenses of travel. The obligation to purchase at market price is equivalent to being able to use the water itself, preventing a shift to the substitute (tayammum), similar to when an item is sold for its exact value, or regarding the slave in expiation for *Zihar*. Furthermore, the harm related to property loss is less severe than harm to life, and since a sick person is obligated to perform Ghusl unless total destruction is feared, accepting minor financial harm is more probable.
Supporting text
Al-Shafi'i holds that it is not obligatory to purchase water even if the price increase is minor or significant. One view concerning a significant but unaffordable price increase suggests it is obligatory to purchase because the person has found the water and is capable of using it, following the principle derived from Quran 5:6. Another view suggests it is not obligatory due to the significant financial harm incurred, similar to the case where one fears a thief taking that amount of money.