Tap water that's drinkable straight out of the tap is a rarity in the world and not really a thing in any developing country. There are certainly parts of China where you could get away with it, but you could get sick in many other places. The issue is that pipes leak here and there, so even though water comes out drinkable from the plant, there's no guarantees what it will be like at the tap. From the perspective of the Chinese, you drink less than 1% of the tap water you use, so why bother making all of it drinkable? But I'm sure things will change as the country develops.