When eating anything that is not recently fried (salad, ceviche, fruit, bread), I take two shots of tequila, one before and another after.
I drink beer instead of water at the restaurant, unless I bought the water myself at the grocery store.
The way to stay healthy in Mexico is almost the opposite of what it is in the US.
Lastly, I'll add that if you can't drink alcohol, maybe you shouldn't go to Mexico. I tried not drinking once in my many visits to Mexico, got an H pylori infection (as a consequence, I believe), and was miserable for about 4 years thereafter. First, that bug is not common in the US so in my case it wasn't properly diagnosed until my 3rd doctor visit. Then, after I got the antibiotics to kill the bug, my intestinal track became hypersensitive and I couldn't digest milk or bread (glutten) properly. After much trial and error and many other doctors visits, I figured out a treatment that involved pro biotics that got rid of much, though not all of the hypersensitivity.