Yeah, I am conservative. Back in the old days of sailing ships, they carried their water supplies in wooden barrels for months in the tropics. It was famous for algal blooms and critters. However, one should remember that the jolly tars were young, vigorous men who had survived a youth in ports with 18th century sanitation stations. They had the immune system of a turkey buzzard. They also drank their water largely in the form of grog -- 3 parts to 1 part 140 proof rum and a part of lime juice (the original daquiri). Hell, with that mixture you can drink raw sewage.
In our case, however it is easy to be conservative in campgrounds with sources of plumbed sanitized water readily available. Drinking ancient water is no longer necessary. And with our delicate and often ancient immune systems is worth caution.
However, if in doubt, the dilution of 2 parts of water with one part of a good bourbon or scotch may be a wise precaution in the evening.
By the way, Mexicans can get tourista. The Valle de Mexico (Mexico City and environs) has an endemic bug, I forget the name, that causes serious diarreha. Mexicans native to areas outside if it can fall prey to the bug. Mexican urban watersystems are less than isolated from the local soil and its critters. Mexicans who can afford to either drink bottled water, or have special domestic purification systems in their homes. The other folks get a lot of waterborne disease and gain 18th century immunity -- the hard way. They also die early, like the 18th century folks.