Cock up (expensive)

Arrived on site with the caravan in light rain below grey skies.
When setting up the gov couldn’t find the water pump, much searching of cupboards, lockers and the like but no pump.
Found a caravan dealer 10 miles away and went to buy a new one presuming we’d left ours on the site last year when we packed up.
“I think it’s right but can I exchange it if it isn’t ?”
“Oh no because of the risk it has been contaminated.”
So we get back to the van, plug it in, open the sink to flush the air out and there in the washing bowl is the pump.
Sh*t.