Is it a health hazard to use tap water for my dentures in mexico?

Uncertain: If you wouldn't drink it then be cautious i guess. Depends on where in mexico and what is in the water. If concerned you could boil the water (not with the denture in it) for about 5-10 min then use that water to clean the denture.

Would you drink it?: If you would drink the water then use it to clean your dentures. Tap water could be better in mexico than here in the states.