Bismilllah,
Asalamu Alaykom:
“Tayammum is obligatory to be performed instead of wodu’ or ghusl in seven circumstances:
1. Unavailability of water
2. Excused for not being able to reach water
3. Use of water constitutes harm
4. Fear of thirst
5. Scarcity of water for washing
6. Non-permissibility of use of water
7. Time being too short”
May Allah grant you success