I would let the one incident slide.
I do however have a huge problem with this teachers snack/drink policy...
IMHO a teacher has NO right to determine what I send with my chiild for a snack time. If there is a snack-time, then fine, let the kids have a snack. That is an issue of scheduling. If a snack is scheduled, then NOBODY has a right to dictate what another person shoud eat or drink.
You really need to read up on school policy... Some school's do have ridiculous school-wide policies regarding things like "no candy" etc... And, that would be a different issue.
Also, I wonder if this teacher considers water bottles as a drink, the same as juice boxes. I would have a huge problem with the children being given a snack to eat.. which would often be things like salty chips, or dry crumbly cookies, without a drink available to wash it down!!!
I do think that this snack/drink issue is one worth a battle. I would be asking for clarification... in writing, CC to the Principal. (since otherwise, this teacher does not seem willing to respond to parent's concerns...) And, if water is not allowed while the kids are being allowed/encouraged to eat, I would fight it...
This teacher sounds like a real you-know-what...