Other mistake: After Del-boy is finished filling the first set of water bottles with the hose, he moves the rig and sets up some new ones. Now, when he pours, the water doesn't go into the bottles, but rather pours over the side. Despite this, Del continues working as though everything is fine.
Revealing mistake: As Del Boy is talking to Rodney and preparing his bacon sandwich a lingering shadow can be seen, being cast against the kitchen door. This shadow belongs to Uncle Albert, who is waiting for his cue to walk into the kitchen with porridge on his face.