Ghusl does not need water flowing on the body, but needs just making any amount of water reach to every part of the body even by wiping water on all parts of the body. A big scholar in Najaf Ashraf who is Ayatullah Sayyed Muhammad Husain Al-Hakeem said: Ghusl can be performed with one cup of water by putting my hand in the cup of water then wiping over my head, face, neck, right side of body then left side of the body. Making the water touch by wiping to the whole body won't take more than one cup of water.

You can refer to Islamic rules of your Marja' of Taqleed for more details.

Wassalam.