If you care to see the real Mexican rules they have a really well done pdf on-line at
http://www.aeropuertosgap.com.mx/......eguridad/4.PDF

See APÉNDICES A. ARTÍCULOS Y MATERIALES PELIGROSOS PROHIBIDOS for discriptions and even pretty pictures of banned items. As for liquids, only flamable, poison or caustic liquids are banned. You are allowed up to "Cinco litros de bebidas alcohólicas" so long as they are labled with brand name, sealed and not over 140 proof.

But as stated. If the flight is to the US or from a secure area that may also have flights to the US, Mexico must enforce the US water ban whether they want to or not under threat of having their planes denied entry into US airspace. CUN has LOTS of US bound flights. I usually fly out of TIJ if I am flying in Mexico. There are no TIJ-USA flights. I have never had them look twice at my water bottle, never had to take off my shoes, never had to put my toothpaste in a baggie. They do seem to have a "belts off" fetish though.

Even in MEX where I am usually either going MEX-PTY or MEX-TIJ but never MEX-USA, I have never been hassled over water. Once when boarding a flight MEX-PTY I was singled out in the Jetway and VERY thoroughly patted down by some very serious looking Mexican federal agents. Not airport security or corrupt local cops. Real serious professional Mexican federal agents. I assume they considered a TIJ-MEX-PTY-CTG itinerary a little unusual for a gringo and were checking to see that I wasn't strapped down with stacks of $100's taped all over my body running the profits back to my drug lord bosses That was a little disconcerting that I was singled out and they were so thorough but they were 100% polite and professional about the whole thing and I suppose it is a valid concern on that route.