take your battery off and recharge with a car charger, once refitted this should then mean the water pump will work, then check the caravan charger to see if anyone has accidently turned it off.
As said before, the battery is flat (for whatever reason - that needs investigating), but the water pump is a quite high load item (3-4A running, higher amps to start!) and will not function from a flat battery.
You don't give a year for your van, so we can't know what charger you've got fitted.
If the battery has been left completely flat for more than a few hours, it will likely have suffered irreversible damage, and may never fully recover to it's full (or even useable!) capacity even when recharged!
Best to recharge it (with a external car charger) and get it load tested at a garage/battery supplier/ Halfords etc. to see if still in good serviceable order. If still in good order, or a replacement bought, then the van charger needs checking to see if correctly functioning.
Hi there thanks you to everyone that's commented I've found the issue the wiring loom under van has been totally damaged so looks like a new wiring loom if that's possible