Tayammum substitutes for water when water cannot properly be used. The explicit restriction is إِذَا قَدَرَ عَلَى اسْتِعْمَالِهِ
Meaning: If one can use it.
Seeing water beyond reach, or water still harmful in an illness, is not the same as regaining the actual ability to use it.
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Tayammum Materials, Intention, Nullifiers, and Searching for Water
Tayammum substitutes for water when water cannot properly be used. The explicit restriction is إِذَا قَدَرَ عَلَى اسْتِعْمَالِهِ
Meaning: If one can use it.
Seeing water beyond reach, or water still harmful in an illness, is not the same as regaining the actual ability to use it.