It isn't the AG regulation on price gouging, 940 CMR 3.18, because that regulation applies only to petroleum products. It also doesn't seem to be related to the gubernatorial state of emergency.
Our best guess is that the issue is with the item pricing law, MGL c.94, sections 184B-184E which requires price tags on the item or on the shelf (with some exceptions). Presumably, a problem may arise where water is marked at one price but being sold for another. The Division of Standards is charged with enforcing "the item pricing law and the unit pricing regulations."
You can find more laws and regulations regarding item pricing at:
- MGL c.6, s.115A Unit Pricing of Packaged Commodities
- 202 CMR 5 Unit Pricing and Checkout Systems
- 940 CMR 3.13 Pricing