Anyone who becomes Junub (a state of major impurity) as the result of a wet dream or intercourse has to do Ghusl. If you cannot do Ghusl because there is no water available, or because you are unable to use it, then you should do Tayammum and pray. In your case, you have to repeat the prayer because you did not do Ghusl or Tayammum.

Ghusl is not required in the following cases: 1- every time one is going to meet people – it is encouraged to do Ghusl beforehand, 2- when undergoing any physical change, 3- for some acts of worship, such as doing Ghusl when entering Ihram.

1. Washing the parts of the body in order and consecutively when doing Ghusl is not obligatory according to the majority of jurists. 2. The more correct scholarly view is that rinsing the mouth and nose is obligatory in both Wudu and Ghusl. 3. If a man or woman does Ghusl to remove major impurity, this Ghusl counts for Wudu too. 4. Wudu and Ghusl are valid even if any bits of food remain between the teeth, but removing them is better.