[weinzierl]

Safety is always a trade-off. If I am in an area with cholera epidemic I gladly will consider the chlorine in my drinking water safe. Where I live the water is clean and adding chlorine does make it definitely less safe.

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.

[radlad]

The TLV you cherry picked refers to concentration in breathable air, not drinking water.

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.

[weinzierl]

"The TLV you cherry picked refers to concentration in breathable air, not drinking water."

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

[radlad]

> That point is that with clean drinking water chlorine is unneccessary as evidenced by all developed countries except the US, Sinagpore and Canada.

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.

[weinzierl]

I think we just have different opinions what safe drinking water means and I won't repeat the arguments and sources from my previous comments, with one exception: I'd like to stress again the point I already made, that even the SDWA encourages alternative water treatment methods now.