You need drinking water no matter where you go, but not all parts of the world can always guarantee clean, safe tap water. This handy guide shows you where drinking from the tap is OK, and where you're better off doing further research on the subject.
The guide from Danny Ashton at NeoMam Studios uses information gathered from the United States Centres for Disease Control and Prevention. You can see each continent with guaranteed safe countries in blue and potentially unsafe countries in brown, along with some tips for how you can avoid unsafe water. Keep in mind, potentially unsafe means that it could be harmful to drink if your system is not used to that environment, not necessarily that the water is polluted and dirty.
It's important to be careful about things like this. Andrew Zimmern of Bizarre Foods will literally eat anything, but he has a rule that he won't drink local tap water in most countries due to not having the immunity locals might have. Avoid the potential microbes and illness, and you're bound to have a much better trip.