How correct is my intuition that tap water is safer in the mountains than in cities?

This probably won't apply to Europe, but I live next to this awesome lake, and a friend of mine actually own a water bottling company!

Above is the Kandy lake, which is located right next to a few mountains. We don't even touch this water.

However, I still think it's somewhat safe to assume that you can drink water that is right next to a mountain.

The above image is of Seetha Gangula, which translates to English as the river of cold water. You can drink this water!

The difference between what you can drink and what you can't is based on the source of the water. Water from rivers are a big no no, but with a significant effort, you can find springs, which provide the best tasting water you'll ever find! It's never pure H20 (which tastes terrible by the way), but loads of minerals mixed to it.

There are two types of natural water bottling types: Spring water and Mineral water.

Spring water must be collected at the source (spring), and after a quite a few purification, you can safely drink that water. But the truth is, this purification process hardly makes a difference. Spring water, if collected in a hygiene way, is good to drink right away.

My friend owns a bottling company that produce mineral water. This usually refers to water taken from a river, and after heavy purification.

Government health departments usually require both of types to be purified first.

As for lakes (my first photo above), people put all the garbage there (animals will become garbage at least), and since the water isn't flowing, it is not safe to drink them at all.

The advice that water in cities is more likely to be drinkable is based on that larger urban water systems tend to have some degree of water treatment (i.e., chlorination, ozone, or UV-based) that will kill bacteria, viruses, parasites, and spores. However, the water source itself may be of questionable quality from the perspective of other pollutants (heavy metals, pesticides etc.).

Rural tap water may not have any sort of water treatment and be pumped straight from the lake or aquifer. The water could easily be a source of giardia or other parasites. That said, lakes in high mountain regions are likely to be free of industrial pollutants like mercury, pesticides, and fertilizers.

tl;dr:
City water == may be polluted with industrial chemicals but may be treated and relatively free of infectious pathogens.
High mountain water == clean of chemicals but may have infectious pathogens.
Low rural areas == may have both agricultural runoff as well as pathogens

Solution: In cities and low rural areas, buy bottled water. In mountain areas, bring your own UV or chlorine/ozone tablets and treat the tap water anyway.

I have a UV SteriPen which I use hiking or in countries with iffy water treatment systems. Note that this advice applies to places where tap water is considered suspect -- notably, mainland Asia, SE Asia, S. Asia, parts of sub-saharan Africa, rural Latin America, etc.

Here in Colorado just about all the rivers, even little creeks, have giardia spores in them. Giardia is really a tough thing to kill. Just boiling the water won't do it. There are some very tiny filters that can, but you have to be very gentle with them or the filter breaks.

The DEA has halted sales of iodine, which could purify water, because iodine can be used in meth labs.

I want to guarentee you that you'll have a really rough time if you get giardia. It's like the worst GI problem you've ever had X a million. Go far out of your way to avoid it.

City water tends to be chlorinated and goes through things like sand that effectively strip stuff like giardia out. While we have a cabin in the mountains, we bring up 5-10 gallons of water when we go there, even though there's a creek 50 feet away from the cabin.

thanks, Dave Small