Purity: Insufficient Water for Ghusl and Wuḍūʾ
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 458:
If the amount of water that is available is not sufficient for performing both wuḍūʾ and ghusl and it is sufficient for performing only ghusl, a woman must perform ghusl, and it is better that she perform tayammum in place of wuḍūʾ. If the water is sufficient for performing only wuḍūʾ and not for performing ghusl, it is better that she perform wuḍūʾ with the water and then she must perform tayammum in place of ghusl. If she does not have sufficient water for performing wuḍūʾ or ghusl, she must perform tayammum in place of ghusl, and it is better that she perform another tayammum in place of wuḍūʾ as well.
-Ayatullah Sistani, Practical Laws of Islam, Purification (Taharah)