Why can't the piercing wait until summer is over? Then you don't have to worry about how contaminated the water is or isn't.
I would be more worried on how dirty the piercing gun or needles were and did the operator wash and disinfect their hands before the proceedure. If an operator went from the counter to the peircing gun without washing their hands, I'd head for the exit quickly, very quickly!
Good luck to you and yours.