Answer
(Fatwa: 71/54/H=1433)
If it is temporary disease then he should intend that as soon as he gets cured he shall do the qaza of all missed fasts. But if the disease (excess of thirst) is prolonged and does not hope to get rid of it till death then he should pay the fidya of fasts and do taubah, istighfar and zikr regularly along with reciting the holy Quran and durood. Also he should pay other rights pertaining to Allah and His slaves as well as keep himself aloof from all sins, and be steadfast in taqwah and taharah, then in-sha-Allah his rewards shall not be decreased.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband