Why is water is leaking between the manifold and the pump body?

The likely reasons for this are worn seals, loose connections or worn high-pressure oO-rings. This is a situation that requires disassembly of the pump and manifold. If your unit is under warranty, take it into the nearest Campbell Hausfeld service center. If it is not under warranty, you should take it into the nearest service center or call Campbell Hausfeld Technical Support at (800) 543-6400