What Would You Do In This Situation?

My son is 7 and just finished his last term in the infants.

Children are allowed to bring home and keep the water bottle, that the school had provided them for the last year, the teachers are meant to wash these up after each day.

I am fuming that my child has been made to drink out of this, but my partner feels it’s pointless kicking up a fuss when our child will be going to the junior school, which is not attached to the infants.

I feel I should keep these pictures and the bottle and show it to them next term to prevent another child having a similar bottle and mould again.