As you may know, there are 2 systems in your trailer.
A 12 volt
pump operated system that pumps the water from your trailer's tank into your faucets/toilet/shower. This requires that you turn on the water pump switch, then try your faucets. It also requires a working battery.
There is also a system that uses water from a domestic supply such as your home water system. To access this, hook up a hose to the trailer at the rear bumper. turn the faucet on and check the trailer operation.
This may be info that you already know, if so I appologize. I don't know what your experience level is.
If you have more questions, ask away.