I've been wondering about the safety and quality of the tap water in my city. I've always been assured that it's clean right out the tap. But I spent this past year living rurally with a groundwater well on-site, and when I visited the city I was struck by how bad the tap water tasted to me.

Given its frequency of use in all our lives, I am generally surprised by the lack of discussion around water quality in my circles. It seems like nobody talks about it, and almost everyone I know drinks (and cooks with etc) what I now consider bad-tasting tap water. Does anyone have good leads or resources on this topic? I'd like to learn more and am unsure where to look first.

Some questions under consideration:

  • What is 'safe' to drink?
  • What makes water quality good vs bad?
  • Are taste and safety/quality correlated?
  • Any recommended water quality tests?
  • To filter or not to filter?
  • Which filtering methods actually work?
  • What questions would you be asking?
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Well my wife is water chemist and has been known to identify water from different treatment regimes by their taste. There are a lot of possibilities here. Bore water is highly variable depending on the aquifer geology. Where groundwater goes through peat, it can be quite acidic (sometimes treated with caustic soda in town supplies) and this seems to appeal to our taste buds. Dissolved minerals obviously also affect taste (for good or bad - I dont like water with lime). By contrast city water supplies would struggle to get enough water from bores and often rely on river or lake sources. Unlike many types of borewater, this is not safe unless treated, generally by chlorination. Tastes terrible in my opinion and reactions between chlorine and organic material can create truly foul flavours and smells. 

The good news is that you can remove the flavour/smell of chlorine with cheap, under sink carbon filters. Just be sure to replace filter regularly.

I would be very surprized if you cant get results of regular city water tests from local authority. If not, then I would make stink as should be public information. I would bet on city water being safe from pathogens (but not necessarily from heavy metals) - it is some peoples job to ensure that with massive consequences for getting it wrong. So much so, that all too common for authorities to just chlorinate even when primary source is safe to protect against possible contimination in the distribution network.

Reverse osmosis (RO) is gold-standard. I prefer the taste to that of our mineral-heavy local rural water. AmazonBasics has a ripoff that's cheaper but I used Brondell Circle which was easy to install (just need to drill or poke a hole in drainpipe, and an opening in counter to place the faucet, which you may already have or could be cut with a circular cutting bit or jigsaw)

Don't have all the answers, but one thing I've been advised against is consuming hot tap water.

The idea is that heated water is generally hot enough to cause various weird things to leach out of the pipes. Theoretically this isn't an issue except lots of pipes have quality control issues or are just old. So if you're going to drink tap water, drink cold tap water. If you want hot water to drink, heat cold water.

Besides that I've long use bottled spring water as my main source of drinking water, but I admit this is largely taste preference (I grew up in a place in Florida where the tap water was the same spring water they bottle and sell).

I had always been told that the "don't drink from the hot tap" taboo, especially in regions that follow the British tradition of separate hot an cold taps, was due to to historical problems with Legionella.

The NYT repeats the claim that hot water should be avoided because it dissolves contaminants, but sadly doesn't cite any sources there. It does align with the general "stuff usually dissolves better in hot water than in cold" observations from daily life, though.

With a UK-style arrangement, where hot taps give you water that's been stored in an internal tank in your house rather than coming straight from the water main (... actually, is that particular feature UK-only? Unless you have "on-demand" water heating, which is I think generally not very efficient, your hot water will have to have been stored somewhere, no?), it seems to me that in addition to Legionella you should be concerned about (1) other nasties growing in your water tank and (2) increased leaching of contaminants not only because the water's hot but also because it's had more time for the leaching to happen.
I think the main difference between UK and US hot water systems is the pressure. They both involve pre-heating a tank. In the UK it's common for the hot water tank to be at atmospheric pressure, so the pressure at your hot taps is from the height of the tank above them. In the US, the hot water system is more usually sealed and at mains pressure.
The noteworthy bit of the UK arrangement is the habit of having 2 taps per sink, not the habit of having a hot water heater at all. I am not aware of any cities with municipal hot water supplied in the way that cold water is -- the closest thing I know of is steam systems that can supply heat to large areas, but I've never seen anyone suggest drinking the water from those. Steam hot water heaters are available to purchase, which suggests they might be used in areas with steam for heat. Most places I've stayed in the continental US have had each building's hot water provided by a heated reservoir of some sort. The off-grid options I've seen are the high-tech on-demand water heaters you mention, or the old-fashioned wood stove water jackets and solar roof heaters. When I've asked friends who drink or cook with hot tap water why they're ok with doing so, their answers have been along the lines that the risk of harm is relatively tiny in modern homes with everything built to code, compared to the convenience of having the water boil that little bit faster. I'll keep my cultural superstition of only drinking from the cold tap, but I do see where they're coming from in reasoning that they know that newer plumbing doesn't contain any of the "really bad stuff" like lead.

So if you're going to drink tap water, drink cold tap water. 

Or buy a water faucet that heats the water instead of taking warm water from a pipe. It also has the other benefit of giving you warm water immediately and a faucet that tells you about the temperature of the water.

The Wirecutter recommends the Tap Score water quality test as being both accurate and with easy-to-understand results.

Where I live, the city also runs its own tests and sends the results to residents, although that would only tell you how good the water coming from the treatment plant is and not if you have problems with your own pipes.

It seems like lead pipes are uncommon after 1950, but if your city's test results are good and you just want to check lead, there are also cheap lead-only tests.

For effectiveness of filtering, it would probably depend on what you're trying to filter out. When I lived in Baltimore, a standard under-sink filter worked well enough to make drinkable tea but it still didn't taste a good as Colorado water.

  • What is 'safe' to drink? What makes water quality good vs bad?

The WHO has a 595-page PDF that probably contains more than you ever wanted to know about it.

Also note that water that's "safe" to drink for a person accustomed to it may be unsafe to start drinking suddenly. There's definitely some survivorship bias involved, but plenty of areas around the world have water that makes tourists sick but is tolerated by the locals.

  • Are taste and safety/quality correlated?

Correlated, sure. Most bad-tasting water will be bad for you; most safe water will taste ok.

Bad taste, bad safety: stagnant swamp, sewage, seawater. Good taste, bad safety: well water contaminated with trace amounts of lead or coliform bacteria Bad taste, good safety: over-steeped tea, boiled water cooled to room temperature

  • Any recommended water quality tests?

If you want a test, you can buy them online. Testing municipal water might be useful to tell you about what's getting added by the plumbing in your home or could help you dial in how much you trust your municipality's water quality reporting.

When I've lived in areas with municipal water, there have occasionally been boil water advisories because the water utility detected bacterial contamination in the water supply. This type of prompt detection and temporary mitigation requires ongoing testing and communication rather than a one-time test kit.

  • To filter or not to filter?

Depends on what you expect will be in your water and how much you care about drinking it. If your municipality's safety guidelines allow a higher level of some contaminant than you're comfortable with, and you detect that it's actually present in your water, you'd probably want to attempt to remove it.

One thing to mention if you're going More Dakka on optimizing your drinking water purity is that there exist tabletop distillation machines designed for home use, although distillation is an extremely energy-intensive process.

  • Which filtering methods actually work?

The effectiveness of a filter depends on what you're trying to remove from the water, the quality of the filter, the condition the filter is in, and whether you use it correctly.

One way to think of filtration is that the rural well water you were drinking before was distilled (evaporated and then fell as rain) and run through an extremely large biofilter (the soil) before it was stored in the underground aquifer that the well tapped into. This demonstrates that there exists an extreme of filtration which gives the water the traits you prefer drinking. The question then becomes "which filtering methods are feasible and yield worthwhile improvements to water quality at the home scale", which depends on your personal definitions of "feasible" and "worthwhile".

  • What questions would you be asking?

I'd be asking what contaminants my municipality tests its water for and what levels they consider acceptable.

I would consider phoning the water provider and asking them very nicely "hey, I'm sure you get this a lot, but I spent some time on a farm lately drinking well water and now that I've come back I notice that the tap water smells/tastes pretty distinctive here. Could you help me understand why that is?".

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I don't have a full answer, but I would expect taste to correlate much more with the water's particular mineral content than anything to do with its safety. Different areas will have water that travelled through different rocks, and picked up a different profile of dissolved minerals.

Agreed: if the city tap water tastes bad, it could as easily because it has less of things you like the taste of as that it has more of things you dislike the taste of.

(Another possibility: the city tap water may be chlorinated. If this has any impact on taste it's likely to make it worse, but it makes it less likely to contain waterborne bacteria that could be bad for you.)