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 .