Residual levels show 3 mg/L of chlorine in the United States which is higher than most other countries (Singapore, and to a lesser extent, Canada, excluded.) What I don't understand is why you see these levels, which are considered safe by most health agencies, as a cause for concern. As another commenter pointed out, the chlorine exists to ensure the water is safe to drink.

The European Union is not a country and it is not surprising that it has no guideline, because the member states have. That the United Kingdom and Ireland are similar to the US is not surprising. I could not find a source for the value of 5 mg/l for Germany, most sources say 0,3 mg/l but the actual text of the current law doesn't corroborate that. What it does is strictly regulate the reaction products of chlorine, which makes sense from a health standpoint.

"Residual levels show 3 mg/L of chlorine in the United States which is higher than most other countries (Singapore, and to a lesser extent, Canada, excluded.)"

I am not a native English speaker, so forgive me if I read this wrong, but the paper says of all the considered countries the US has higher residual chlorine levels than all the other countries (Singapore, and to a lesser extent, Canada, included)

In other words US is highest, followed by Singapore and then Canada.

"As another commenter pointed out, the chlorine exists to ensure the water is safe to drink."

As the paper shows most developed countries have safe drinking water without chlorine. So the question is not why I am against it but why the US needs it in the first place .

Chlorine is a very hazardous substance after all.

According to the CDC the TLV for chlorine is 1.5 mg/m3. Note, that this is per cubic meter and not per liter. So a TLV of 0,0015 mg/l vs 4 mg/l in US drinking water.

https://www.cdc.gov/niosh/idlh/7782505.html

And here the definition of TLV from Wikipedia:

The threshold limit value (TLV) is a level of occupational exposure to a hazardous substance where it is believed that nearly all healthy workers can repeatedly experience at or below this level of exposure without adverse effects.

Most health authorities agree that chlorine is safe at 4 mg/l.

Ultimately proactive and reactive approaches both have pros and cons. But implying levels of chlorine in US drinking water are unsafe has no scientific backing.

Chlorine is a gas. I started this subthread with my claim that I always experienced a smell of chlorine in American tap water. Now the threshold to smell chlorine is 3 ppm while the TLV is 0.5 ppm. In other words, when you can smell it is already way above the TLV.

But it is even worse: While chlorine is absorbed when ingested, this is a lesser problem. Copyed from my comment above: "Chlorine forms compounds with organic substances (the microorganisms it kills) in the water, which in turn can be toxic or carcinogenic. Instead of regulating the (volatile) chlorine it makes much more sense to regulate the harmful compounds, which is exactly what many European countries do."

"Most health authorities agree that chlorine is safe at 4 mg/l."

Authorities agree that chlorine is safer than dying from the pathogens in dirty water. We all agree on that. If you have the choice of dying from cholera next week or bladder cancer in 15 years, you sure will pick the cancer. (Yes, there is a link between chlorinated drinking water and bladder as well as colorectal cancer).

Safety is always a trade-off and the EPA's task is to find a compromise [1]. That is where the 4 mg/l come from. Other authorities and organizations have different priorities, which result in different thresholds. For example, The International Botteled Water Association limits chlorine in botteled water to 0.1 mg/l. In Germany, the level for water in swimming pools is 0.3 mg/l. And by the the way the current SDWA encourages alternate treatment methods too.

Ultimately proactive and reactive approaches both have pros and cons. But implying levels of chlorine in US drinking water are unsafe has no scientific backing.

It is not about proactive and reactive approaches. That point is that with clean drinking water chlorine is unneccessary as evidenced by all developed countries except the US, Sinagpore and Canada.

[1] "EPA must conduct a thorough cost-benefit analysis for every new standard to determine whether the benefits of a drinking water standard justify the costs." https://en.wikipedia.org/wiki/Safe_Drinking_Water_Act

And once again, whether necessary or unnecessary, the original question was whether the water supply is safe to drink in the United States. And - at least in regards to municipal water (houses on well, e.g. in rural areas, obviously vary) - it is.