to not use plastic school bottles?

[DropItLikeASquat]

I have 4 children at primary school. The school has introduced a new rule that all drinks bottles have to be clear plastic so they can recognise if children are bringing 'contraband' squash to school. now, just a few weeks ago I invested in so good quality stainless steal water bottles and I have said I'm not buying new ones. One of my children teaches asked me why I feel I can single out my children.
I explained that the rate that my children go through the plastic school issue bottles (at £3 a bottle) is making it quite unaffordable and I am also conscious of the amount of plastic waste that we re generating as a family.
She replied to say 'well how are we the know that they are not bringing squash?' I explained that my children only ever bring water and I firmly reiterated that I will not be purchasing the plastic ones.
AIBU to do this? I know of 2 other families at the school that are also refusing to use the school bottles for similar reasons to myself and they too have been met with the same hostile questioning.
Thankyou for your replies.

If you wait a bit too they have just had a 15% off promotion and will likely have another after half term so you will get them even cheaper.

I couldn’t give the tiniest shite what the kids in my class have in their water bottles. Well, not red bull/ gin and tonic etc but you know what I mean. The bottles live on the draining board by the sink, so spillages are a non-issue. Yes I know I’m lucky to have a sink in the classroom.

Thanks! I’ll have a look