The question is a little unclear. If your RPod has a tank style water heater, it is a six gallon model. The limiting factors are in how much you want to use and how quickly you want to use it. Separate, but related is whether you are drawing from your fresh water tank or connected to an external water source. 

The six gallons will be enough for a shower, especially if you pause the water flow after getting wet and then finishing with a rinse. The water heater recovers fairly fast on propane and still pretty fast on electricity.  It would not be enough to fill a standard bathtub, which would not be in your Rpod anyway. It will be enough to wash dishes.

The limiting capacity is if you are not connected to full hookups, to include sewage drain. Your grey water tank will fill pretty fast, so if you are boondocking, you need to take black and grey water tank capacities into account as well.