Is the Water Safe to Drink?
"The Manager has personally passed all the water used here." - A notice to guests posted in an Acapulco Hotel
Bad translations aside, Mexican water is famous around the world for not being safe to drink. "Don't drink the water" is the common refrain. The reputation of Mexico's water has indeed been earned. You can travel to all the continents in the world -- including Africa -- and not run into the problems that can become commonplace in Mexico.
The full answer to the question whether it is safe to drink Acapulco's water is that it depends a good bit on where you're getting your water. Generally the water is safe to drink if it has been purified. Otherwise, it's not safe. In other words, the water they serve you, or that you buy in bottles, is fine, but water from the tap is not. The exception is that some of the finer hotels filter and treat their tap water, too. But as a general rule, no one -- not even the local residents -- drinks tap water.
If you are wondering what happens if you drink the tap water, go to the article on Montezuma's Revenge.
So what actually causes the problem? Bacteria. Candidates are E. coli, Salmonella, Shigella, Campylobacter, Aeromonas, Plesiomonas, and vibrios. What else? Parasites like Giardia, Entamoeba histolytica, Cryptosporidium, and Cyclospora. Any thing else? Viruses.
In tourist zones, no one will serve untreated water. Everyone in Acapulco (indeed in Mexico) knows better. Serving someone water, ice, or food prepared with untreated water is tantamount to walking up to them and giving them a big kick in the stomach. The water and ice are purchased from purveyors who bottle and bag their product using treated water.
Street vendors and low-end restaurants might use a little tap water in the preparation of their food, but usually this is not enough to affect the stomachs of their clients. Most of the time it is boiled or cooked before serving. Be forewarned: the clientele of these places are mainly locals who have lived in Acapulco most of their lives.
Most of the time, people get sick just because they (or someone else) puts unwashed hands into a bodily orifice, like the eyes, nose, mouth, et al. Then they blame the restaurant food. The lesson: Wash the hands regularly or use the sanitizing alcohol-gel on the hands. And be careful! As they might say in Mexico "¡Ojo!" or "¡Aguas!" (literally, "eye" and "waters"), which both mean, "watch out!"