Tayammum is allowed when there’s no water available, whether you’re traveling or at home. The condition is: taharri (search and effort to find water). In case you don’t find water and you had to do wudhu/ghusl for prayer, you may do tayammum.
Narrated ‘Abdur Rahman bin Abza:
A man came to ‘Umar bin Al-Khattab and said, “I became Junub but no water was available.” ‘Ammar bin Yasir said to ‘Umar, “Do you remember that you and I (became Junub while both of us) were together on a journey and you didn’t pray but I rolled myself on the ground and prayed? I informed the Prophet about it and he said, ‘It would have been sufficient for you to do like this.’ The Prophet then stroked lightly the earth with his hands and then blew off the dust and passed his hands over his face and hands.”
The procedure is also mentioned in this Hadith. We’ll discuss it later though inshaAllah.