When absolutetly no water is available, you should perform Tayammum (dry wudu)...
Hadith - Bukhari 1:331, Narrated Jabir bin 'Abdullah
... The earth has been made for me (and for my followers) a place for praying and a thing to perform Tayammum, therefore anyone of my followers can pray wherever the time of a prayer is due.
The Noble Qur'an 5:6
O you who believe! When you intend to offer As-Salāt (the prayer), wash your faces and your hands (forearms) up to the elbows, rub (by passing wet hands over) your heads, and (wash) your feet up to ankles. If you are in a state of Janāba (i.e. had a sexual discharge), purify yourself (bathe your whole body). But if you are ill or on a journey or any of you comes from answering the call of nature, or you have been in contact with women (i.e. sexual intercourse) and you find no water, then perform Tayammum with clean earth and rub therewith your faces and hands. Allāh does not want to place you in difficulty, but He wants to purify you, and to complete His Favour on you that you may be thankful.
The Procedure for Tayamum is:
Declare the intention that this act is for the purpose of worship and purity. Touch earth, sand, or stone lightly with both hands and then wipe the face with them once as done in the partial ablution.
Touch earth, sand, or stone lightly with both hands and then wipe the right arm to the elbow with the left hand and the left arm with the right hand.