Ruling 658 — Purification (Ṭahārah)

If using water would result in a person dying, or it would make him ill, inflict him with some defect, prolong an illness he has, or make his illness worse or difficult to treat, then in all these cases, he must perform tayammum. However, if one can reduce the harm of using water – for example, by heating it – he must do so and thereby perform wuḍūʾ or ghusl as required.