Firstly: Unavailability of Water Physical unavailability of water
From the conditions of dry ablution is for there to be a physical unavailability of water. Consensus has been quoted over this by: Ibn `Abd al-Barr, al-Nawawi, and al-Shinqiti. Presence of insufficient water
Scholars have differed over what to do if a person has access to water that is insufficient for his purification according to two views:
The first: is that he uses the water for as much of ablution as possible, then to perform dry ablution for the rest of body parts the water was insufficient for. This is the position of the Shafi`is, Hanbalis, and a group from the Salaf. It is also the choice of Ibn Hazm, Ibn Baz, and Ibn `Uthaymin.
The second: is that if there is insufficient water to start with, then the person performs dry ablution and there is no need to use the water. This is the position of the Hanafis, Malikis, the old position of al-Shafi`i, and a group of the Salaf. It is also the choice of Ibn al-Mundhir, and is narrated by al-Baghawi as the most common view among scholars. If a person in a state of hadath only has enough water to remove najasah from his body
If the water is sufficient solely for the removal of najasah, then the person should use it to remove it and then perform dry ablution after that from his hadath. This is the position of the majority: Hanafis, Shafi`is, Hanbalis, a position among the Malikis, and the position of Dawud al-Zahiri. If there is water that is needed for drinking
Whoever has sufficient water solely to drink, then his obligation is to perform dry ablution. Consensus has been quoted over this matter by: Ibn al-Mundhir, al-Kasani, and Ibn Hajar. If a person performs dry ablution forgetting water is there
Whoever performs dry ablution forgetting that there is water available, then he must repeat any prayers he has prayed during that period. This is the position of the majority Malikis,  Malikis made it as a condition for repetition that the prayer is still within its time. If its time of validity has left, then there is no repetition necessary. Shafi`is, Hanbalis, and Abu Yusuf from the Hanafis. The ruling of asking for water
It is wajib to ask for water before dry ablution, except if there is certainty in its unavailability.  Some scholars have estimated the distance within which it is wajib for one to ask for water as one mile, others have mentioned less than two miles, whilst others said that being close or far comes back to custom. If he performs dry ablution before asking, then this does not suffice him. This is the position of the majority: Malikis, Shafi`is, and Hanbalis The time of asking for water
It is wajib to ask for water once the time for the prayer has entered. The majority of scholars have mentioned this explicitly: Malikis, Shafi`is, and Hanbalis. Whoever believes for certain or most likely that there is water but at the end of the prayer time Inability to use water due to cold, fear, or illness
Whoever is unable to use water due to cold, fear, or illness,  Al-`Ayni said: “Scholars consensually agree that if someone scares destruction over himself, or one of his bodyparts, then dry ablution is permissible for the.” Al-Binayah Sharh al-Hidayah (517/1) is allowed to perform dry ablution. This is by agreement of the four schools of jurisprudence.
Secondly: The Entering of the Time for the Prayer that Dry Ablution is Performed for
Scholars have differed over whether it is a condition for dry ablution to be performed after the time of the prayer it is performed for enters, and this is according to two views:
The first: is that it is a condition for the prayer’s time to enter. This is the position of the majority: Malikis, Shafi`is, and Hanbalis.
The second: is that it is not a condition. This is the position of the Hanafis, Zahiris, a narration from Ahmad, and the position of some of the Salaf. It is also the choice of Ibn Taymiyyah and al-Shawkani.
Thirdly: The Purity of What is Used for Dry Ablution
It is a condition that what is used for dry ablution is pure. Consensus has been quoted over this by: Ibn Qudamah, al-Nawawi, Ibn Taymiyyah, and al-Kamal ibn al-Hammam.