I think the Thai officials did a press conference a few years ago to declare the Bangkok water safe to drink, but I still wouldn't do it. They and other Thais probably have a lot more bacterial immunity. I probably get the runs nearly every time I go anyway, but much less fun is the more serious constant-pain bit where your immune system has to use all your energy to fight off whatever it is. That one can have you bedridden for a day or two and weakened for another day or two. I've had that maybe 7 times (including a shingles attack, but most were foodborne like the Bali belly). So that's the risk I usually weigh against the effort needed.

As for Pattaya, back in my first visit in 1992 the water was so yucky-brownish I took a picture to show people back home (alas, back in the film era...my greatest trips were in the last years of the film era).