The practice of the mark of bondage can be done by either controlling the marks they have made before or trying to create new ones. They chose to try to create new ones because controlling the previous ones would torture their slaves too much.
Trying to create new marks is energy intensive, but the progress towards increasing their proficiency is also faster with it. Besides, they don't have to worry about the expenditure of spiritual energy when they have energy water.
When they run out of energy, all they need to do is open the keg and drink from it. They felt refreshed immediately after drinking the energy water. Their minds became clearer and more active.
Drinking energy water won't give them the total energy contained within it instantly. Energy water will only have an exponential effect on the regeneration of spiritual energy.
