First:

When it is not possible to procure sufficient water for performing Wudhu or Ghusl.

655. If a person happens to be in a populated area, he should make his best efforts to procure water for Wudhu or Ghusl till such time that he loses all hope. And if he happens to be in a desert, and if the land is uneven, he should search for water in all the four directions for a distance covered by one fling of an arrow, and if the land is even, he should search for water in all four directions for a distance of two flings of an arrow.

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.

658. If the time left for Namaz is not short, and if he is sure or feels sure that water is available at a farther place, he should go there to procure water. And if he has mere suspicion about water being there, then it is not necessary for him to go.

659. It is not necessary that a person should go himself in search of water. He can send a reliable person for this purpose, thus, it is sufficient if one person goes on behalf of many.

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, as a recommended precaution, he should search for water again, 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, as per recommended precaution, 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 in order.

665. If a person is sure that he cannot get water and therefore, he does not go in search of water and offers his prayers with Tayammum, but realizes after prayers that if he had made an effort he would have fetched water, the Namaz he offered is void.

666. If a person could not get water after a search and prayed with Tayammum and then learns later after offering prayers that water was available at the place where he had searched, his prayers is valid. If he comes to know about the presence of water, as per precautionary measure, he should offer his prayer again.

667. If a person believed that the time left for prayers was little, and prayed with Tayammum without going in search of water, but later learnt after the prayers but before the expiry of time that there was time for a search of water, then the obligatory precaution is that he should repeat that prayer.

668. If the time for Namaz has set in and a person is already with Wudhu, he should not allow his Wudhu to become void if he knows that he will not be able to find water or he will not be able to do Wudhu again. He should not invalidate his Wudhu deliberately. However, a man can have sex with his wife even if he knows that he will not be able to do Ghusl.

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, as per recommended precaution, he should try to keep his Wudhu intact, and should try to observe the precaution as much as he can.

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 as per recommended precaution, he should not throw it away even before the time for prayers sets in, and should try to observe the precaution as much as he can.

671. If a person knew that he would not get water, and yet made his Wudhu void or spilled it after the time for prayers had set in, he committed a sin but his prayers with Tayammum will be order. However, as per recommended precaution, he should offer the Qadha of the prayers.