Tayammum should be performed instead of Wudhu or Ghusl in the following seven circumstances:
First:
When it is not possible to procure sufficient water for performing Wudhu or Ghusl.
656. If out of the four directions, some are even and others are uneven, one should search for water in the even direction to the extent of two arrow flings, and on the side which is uneven to the extent of one arrow fling.
657. It is not obligatory for a person to search for water in the direction where he is sure that water is not available.
660. If a person feels that there might be some water in the provision he carries or at the place of encampment or even in the convoy, he should search for it thoroughly, till he is satisfied that there is no water or he becomes hopeless.
661. If a person searched for water before the time for Namaz, but did not find it and if he stayed there till the time of prayers set in, he should search for water again, as a obligatory precaution, provided he feels that water may be found.
662. If a person searched for water after the time for Namaz had set in, and did not find it, if he stayed there till the time for next prayers, and if he felt there was a possibility of water being found, the obligatory precaution is that he should go in search of water again.
663. When the time left for prayers is short or when there is fear of thieves or wild beasts or when the search for water is unbearable, it is not necessary for one to search for water.
664. If a person does not search for water till the time for Namaz approaches Qadha, such a person has committed a sin, but the namaz which he will pray with tayammum will be valid.
665. If a person is sure that he cannot get water and does not, therefore, go in search of water and offers his prayers with tayammum, but realises after prayers that if he had made an effort he would have fetched water, his prayers is volid.
669. If a person is with Wudhu before the time for prayers set in, and knew that if he made his Wudhu void, it would not be possible for him to get water, if he can keep his Wudhu intact, the recommended precaution is that he should not invalidate the Wudhu.
670. If a person has just sufficient water for Wudhu or for Ghusl, and if he knows that if he spills it he will not be able to get water again, it is haraam for him to spill it if the time for prayers has already set in, and the obligatory precaution is that he should not throw it away even before the time for prayers sets in.
Second:
672. If a person is unable to procure water on account of old age or weakness, or fear of a thief or a beast, or because he does not possess means to draw water from a well, he should perform tayammum. The same would apply if acquiring water or using it is intolerably difficult.
673. If a bucket, a rope and other similar implements are needed for pulling water out of a well, and the person concerned is obliged to purchase or hire them, he should do so even if he has to pay much more than the usual rate. Similarly, he has to buy the water even if it is sold at a higher price. However, if by doing so, his economic condition is harmed, then it is not obligatory to procure them.
675. If digging a well does not involve hardship the person concerned should dig a well to get water.
676. If he is given water by another person without any obligation he should accept it.
Third:
677. If a person fears that if he uses water his life will be endangered, or he will suffer from some ailment or physical defect, or the illness from which he is already suffering will be prolonged, or become acute or some complications may arise in its treatment, he should perform Tayammum. However, if he can avoid the harm by using warm water, he should prepare warm water and do Wudhu or Ghusl
678. It is not necessary to be absolutely certain that water is harmful to him. If he feels that there is a probability of harm, and if that probability is justified by popular opinion, giving cause for some fear, then he should do tayammum.
679. If a person has an eye disease and water is harmful to him he should perform tayammum.
680. If a person performs tayammum on account of certainty or fear about water being harmful to him but realises before Namaz that it is not harmful, his tayammum is void. And if he realises this after having prayed he should as per obligatory precaution offer the prayers again with Wudhu or Ghusl. And if the time for Namaz has passed he should offer the Qadha of the prayers.
681. If a person was sure that water was not harmful to him, and he did Ghusl or Wudhu, but later realised that water was harmful to him, his wudhu and Ghusl will be valid.
Fourth:
682. If one fears that if he/she uses water for Ghusl or Wudhu, he/she himself/herself or his/her wife/husband or children or friends and dependents such as servants or maids will die or will become ill or will be intolerably thirsty, he/she must perform Tayammum instead of Wudhu and Ghusl and if he/she fears that an animal belonging to him/her will die of thirst, he/she must give the water to it and perform Tayammum. Also, if someone whose life is obligatory to preserve, will become so thirsty that if one does not give water to him/her, he/she will die, it is necessary to give him/her the water and perform Tayammum.also if he fears that person will become thirsty later.
683. If besides the Pak water which a person has for Wudhu or Ghusl he also has najis water enough for drinking, he should keep the Pak water for drinking and pray with tayammum. If water is required for an animal , it should be given najis water to drink and Pak water be used for Wudhu or Ghusl.
Fifth:
684. If the body or dress of a person is najis and he possesses only as much water as is likely to be exhausted if he does Ghusl or Wudhu, and no water would be available for making his body or dress Pak, he should make is body or dress Pak and pray Namaz with tayammum. But it is recommended precaution that he should make his body or dress Pak firstly. and if he does not have anything upon which he would do tayammum, then he should use the water for Ghusl and Wudhu, and pray with najis body or dress.
Sixth:
685. If a person possesses such water or container which is not permitted to use, like when they are usurped (Ghasbi) he should perform tayammum instead of Ghusl and Wudhu.
Seventh:
686. When the time left for Namaz is so little that if a person does Ghusl or Wudhu he would be obliged to offer the entire prayers or a part of it after the prescribed time, he should perform tayammum.
687. If a person intentionally delays offering the prayers till no time is left for Ghusl or Wudhu, he commits a sin, but the prayers offered by him with tayammum will be valid, although recommended precaution is that he should give Qadha of the prayers.
688. If a person doubts whether any time will be left for prayers if he does Ghusl or Wudhu, he should perform Ghusl or Wudhu.
691. If a person has only just enough time that he may perform Wudhu or Ghusl and offer prayers without its Mustahab acts like Iqamah and Qunut, he should do Ghusl or Wudhu, whichever is then necessary, and pray without those Mustahab parts. In fact, if for that purpose, he has to avoid the next Sura after al-Hamd, he should do so after doing Wudhu or Ghusl.