A person must perform tayammum if he needs water to quench his thirst. It is permitted to perform tayammum for this reason in two cases: 1. if one uses water for wuḍūʾ or ghusl, he fears he will presently or later on become thirsty which will cause him to die or become ill, or it will require him to endure excessive difficulty; 2.
one fears for someone dependent on him – even if the person is not among those whose life is legally protected – if the affairs of the person’s life matter to him because of his intense affection for the person, or because if the person dies it will harm him financially, or because it is commonly considered necessary to care for the person as is the case with a friend or a neighbour.
Apart from these two cases, it is possible for thirst to be a valid reason for performing tayammum, but not from the perspective mentioned above; rather, from the perspective that preserving life is obligatory, or because the death or restlessness of someone [due to thirst] would assuredly cause one hardship.