Well, it depends on the source and a few other things. There’s a 1 in 3 (33%) chance that water out of a toilet* will not give you food poisoning, a 66% chance for non-flowing water (like ponds), a 75% chance for non-flowing deep water, a 90% chance for flowing water (river) and a 95% for flowing deep water. But never 9/10, unless you’re drinking sewage (why?!). [Source: I checked the code]
*This gets calculated new every time you draw water out of a toilet.
You could use a funnel to circumvent that problem fully, although the new weather system makes it a lot harder to catch enough water.
You could also use one of the tips from a “survivor’s note”: “I put my toilet water into a gastank. Then I poured it into a glass cup. Then I drank it without vomiting my insides back into the toilet.”
Or abuse some of the game mechanics by drinking something right before the clock turns to xx:30:00 or xx:00:00, as that’s the time (for now) you spontaneously digest it (actually all 5 minutes, but I wouldn’t trust it fully), although I do see it as a bad sign to “fight” a bug by (ab)using the games own code.
Also, if you pour water into a container that contains already known “good” water (test it; if you don’t get food poisoning from your first drink out of that container, then it’s good), it will magically remove any poison - unless that was changed (fixed) at some point.
Yeah, raw water isn’t that “bad”, usually. And, as you said, you don’t vomit every time you get food poisoning.
There’s only one situation when all of that stuff above doesn’t work and you’ll need to cook your water: when it’s frozen .