The World Federation One Stop Fiqh

Ruling 658

If using water would result in a person dying, or it would make him ill, or inflict him with some defect, or prolong an illness he has, or make his illness worse, or make it difficult to treat, in all of 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.