Hazrat Ali (may Allah be pleased with him) says that when a person becomes junub (in a state requiring ritual purification) in a desert and has very little water with him, he should give preference to his life over the water and perform tayammum with earth.

Hazrat Ata and Hazrat Tawus say that when you are on a journey and have only a little water with you, then perform tayammum and save the water.

Hazrat Ibn Abbas (may Allah be pleased with both of them) narrates that if you become junub (in a state requiring ghusl) during travel or your wudu breaks, and you fear that you will die of thirst if you perform wudu, then do not perform wudu and save the water for yourself.

It is also narrated in the same way from Hazrat Saeed bin Jubair.