Turns out my son got hold of the bottle, played around with it, lost/broke/chucked it and that was that.
Fast forward a week later, I had a knock at the door and some guy dressed in white shirt and tie, with a clipboard asked to speak to owner. Not sensing danger I engaged him – whereby he said he had come to collect the water sample. At this point I told him I didn’t have it, and wasn’t interested. His tone changed immediately and demanded the bottle be returned or we’ll have to pay a fine. To which point I laughed and told him to FO, and then closed the door.