I’d imagine the vast majority of garden hoses draw their water from the domestic supply that goes to the taps anyway (but you never know what’s been festering in the hose itself).
In restaurants in the Caribbean, it’s pretty common for servers to bring your bottle of water to the table and carefully open the bottle so that you can hear the sound of the seal being broken, thus proving that they haven’t simply refilled an empty bottle with tap water.
Every locale has unique microbiota. Your body is filled with whatever is in the area you live in. If you travel far from home, you are going to be exposed to different microbiota. This has nothing to do with whether it’s France, so don’t take your French teacher out of context.
Even if the water quality is excellent in France, and perfectly safe, it is not sterile. Some people will experience diarrhea or other GI symptoms as their digestive system makes the adjustment. This is very common and not a sign of a problem with the water supply. The same thing can happen to French travelers visiting Washington, D.C.
On my first trip to Egypt I was warned not to drink tap water. In a moment of dire thirst without access to bottled water, I did, and I had diarrhea for a week. The locals, of course, drink it every day with no problem. The water supply is safe, my body just freaked out when it encountered bacteria it had never met before.
Some countries have poor sanitation that can cause more serious illness in travelers or people with weakened immune systems, but France is not one of them.
At one time ‘Perrier Water’ was everywhere, even in the House of Commons. Then there was the scandale Perrier benzene which practically wiped them out. I believe that most of the bottled water in the H of C comes from Scotland these days.
After about eight years living in Paris (and drinking tap water mainly in coffee, tea and when cooking) I developed kidney stones, but that was probably more to do with diet than anything else.
We had really hard water in Alsace- the death of our electric kettle speedily occurred- but it tasted just fine and never made anyone ill.
On the other hand, the blue-green water at my University in the US…
Never had problems in France, the tap water just tastes strange.
We were in Malta in April and the hotel said not to drink the tap water, and they provided bottled water. Probably got fed up with guests complaining about the water quality and/or traveler’s diarrhea.
I imagine scaring foreigners into drinking wine and bottled water is great for the tourist trade.
One general difference between tap water in different countries might come from the amount of fluoride added to the water: http://https://en.m.wikipedia.org/wiki/Water_fluoridation The USA tend to add quite a lot, while European countries tend to use less fluoride.
That said, France is a country that has fluoridated tap water (but with lower concentration than the US, according to Wikipedia). So concerning this aspect, you might not expect any effect to an American visitor. It might be differerent for countries that have no fluoride in their drinking water (like e.g. Germany). If at all, these might be long term effects on e.g. tooth decay or similar.
In France, just be sure you don’t drink “Eau de Javel” (“Water from the town of Javel”) which is pottasium hypochloride, or bleach… 
Are minerals added to the desalinated seawater, or is it basically just pure distilled water? Because I’ve heard that distilled water tastes sort of “flat”, since we’re used to water with minerals in it.
When we went to Turkey many years ago, we were staying in a small village on the coast. The water in the taps was (supposedly) bacterially safe, but was so full of minerals that it tasted absolutely foul; so bad that we couldn’t even use it for cooking - in the shower, one kept one’s mouth firmly closed.
Cooking water, we fetched from a public tap in another village about 5k away and drinking water was in bottles.
Well, that’s why we mostly drink wine and beer. You know, to be safe.
At least that’s what I keep telling my liver doctor. But I know better, I’ve seen what water does to perfectly good iron over time, I don’t want that stuff anywhere near me !
On a small scale, people who come from towns where the water tastes only slightly mineral (Sydney.aus) sometimes find that water in my home town, which is basically rain water (Melbourne.aus) doesn’t taste right. I mean, people actually buy mineral water, so some people obviously prefer those flavours in some situations. But in Melbourne nobody minds that our water has no flavour.
I don’t know the subject well enough to understand that. Do those ‘Microbiologiques’ categories include Cryptosporidium and Giardia?
I only see bacteria in the linked report. Doesn’t mean they are not testing for other organisms, but interesting that the results are not mentioned. The first link I posted merely says that tap water is the “most highly controlled alimentary product in France”, must not contain disease-causing germs or bacteria [among other things], and that Paris water conforms to 56 parameters defined by the public health code, so it should be easy enough to find out exactly what those parameters are; a 2007 decree is mentioned…
Well, we once stayed at a dodgy vacation home in France, in a little village in the burgundy region. This was in the early days of the internet, when it was harder to tell if someone was selling you a bill of goods on a vacation rental website.
The “gite” was an ancient stone cottage, with lots of centipedes. Both my husband and I drank the water from the faucets there, and both of us came down with bad diarrhea and nausea. I got over it in a couple of days, but he was very sick for a week. We left the gite in a couple of days and went to a modern hotel in Paris, so we could have access to a doctor.
I think it was just a case of getting used to foreign bacteria, as CookingWithGas says. That and I think the plumbing in the little village might not have been as up to date as it could have been.
I’ve drunk loads of tap water and spring water in France and never had an issue. I don’t assume they are lying when they report the city water has zero E. Coli and friends.
In the middle of nowhere in a decrepit cottage, who knows? Maybe they were illegally not up to code. Are such places generally safer in the US?
I did once get incredibly, dangerously ill from accidentally drinking untreated agricultural water in the Middle East (not in a city). Typhoid fever is not fun.
Back in the 40s and 50s, you were warned not drink the tap water in Europe. I think it wasn’t nearly as well controlled as it is now. Your French teacher has absorbed this old meme.
How long ago was high school? Are they old enough to have maybe traveled there sometime in the decade or so after WWII? The French had a couple years in the 1940s where their infrastructure got the Sergeant Hulka treatment in the movie Stripes. (“Blown up, Sir!”) There’s a realistic chance that the rule of thumb they were stating was based on real water quality issues in chunks of the country during the post-war rebuilding.
Potentially your teacher was merely not up to date instead of wildly off base.
Old wifes tales. Or someone mixed France with Egypt. Or water with raw milk.
As for my experience, tap water in EU is in most cases good enough to drink if not specified otherwise. In my (EU) city specifically, they say, tap water can put any bottled water to shame. In fact, large brewery right by the historical center bottles water from its own well and sells it at a price of beer.
Tap water quality really depends on many, many things, like (primary) source: river, rain, well, sea … then general pipe-works and distance from source to end user, tech used, purification methods (if needed) etc. That said, I can see some France sub region can have somewhat flowed water, but it can not be just generalized this way.