AYFKM: Arsenic in Mountain Valley Spring Water

Not that big a deal

Author

Mark Sisson
September 30, 2025

Years ago, I had the idea for a new website called AYFKM. Are you fucking kidding me? It would be a place where I could rant about ridiculous news articles, current events, studies, nutritional research, or anything else that elicits that instant response: are you fucking kidding me? I even bought the domain name, and I still have it.

I figured since I started Untethered, I’d start doing them here.

The latest thing is a new class action lawsuit against Mountain Valley Spring Water for supposed elevated arsenic levels. Before I start, I have to say that I’ve been drinking Mountain Valley for well over a decade. I get it delivered to the house by the case. It’s my go-to water, both sparkling and flat. I probably drink at least one a day. So am I biased? Maybe. But I’m also right.

Here’s the deal. Some batch testing of a single shipment of Mountain Valley Spring Water found that it contained 0.16 ppb arsenic. The EPA limit is 10 ppb for arsenic in drinking water. That’s water they assume you’ll be using for everything throughout the day. Cooking, drinking, showering, washing dishes, etc.

The post from the person who tested the batch mentions that Mountain Valley exceeded the so-called California health guideline of 0.004 ppb. Now that’s an enormous gap: 10 ppb versus 0.004 ppb. Sounds alarming.

Here’s how the OEHHA arrived at 0.004 ppb. They set the limit based on lifetime cancer risk at one excess case per million people. That means, theoretically, if 1 million people were to drink water at 0.004 ppb arsenic for their entire lives, one of them would get cancer at some point in their lives. One in a million. One extra cancer case per million people over a million lifetimes. 

Now, you might say lower is better, and if you can get to 0.004 ppb, why wouldn’t you?

First, it isn’t even practical to measure at that level. I’d say it’s impossible. Even the most cutting-edge methods bottom out around 0.05 ppb.

Second, the potential health benefit of getting down that low is marginal compared to the astronomical cost it would take to get there. You’d have to spend an unfathomable amount of money just to approach it, diverting resources from other public health priorities.

Third, a little bit of arsenic is completely normal. Most public aquifers run between 1 and 5 ppb. All throughout history, people have naturally consumed a small amount of arsenic with every sip of water. Most arsenic is completely natural, entering water through the dissolution of rocks that contain it. There were even historical communities who ate huge amounts of arsenic, claiming they gained hormetic health effects from the practice. A Scientific American article for 1869 confirms this:

Older persons who have been accustomed to that habit from their boyhood feel a sensation of warmth in the stomach shortly after taking the poison, complaining only of dizziness in the head after excessive use. The ratsbane eaters belong mostly to the lower classes, wood cleavers, stable grooms, charcoal burners, and wood warts. They fall into that habit at the early age of fifteen, and continue it until the ages of seventy and seventy-six.

Not something I’d use as medical advice, but it suggests that minute doses of arsenic are compatible with normal lifespans.

Finally, the OEHHA levels of 0.004 ppb aren’t a safe-versus-unsafe cutoff. They’re an idealized, pie-in-the-sky best-case scenario of what health fanatics would like to see if they could press a button. They’re not realistic goals. Not even the people who came up with it would claim it’s what every consumable product should attain. 

So when you look at the 0.16 ppb found in a single tested batch of Mountain Valley Spring Water, you realize that while it’s 40 times higher than the OEHHA’s theoretical guideline, it’s still 60 times lower than the legal limit.

In case you still aren’t convinced, let’s take a look at how many extra cases of cancer the 0.16 ppb of arsenic would produce given the worst case scenario as laid out by the OEHHA. Instead of 1 case per million lifetimes, it would be 40 cases per million lifetimes. That’s a 0.004% absolute increase in cancer risk. Baseline lifetime cancer risk in the United States is 400,000 per million, or 40%. 0.004% versus 40%. We’re talking peanuts. 

0.16 ppb is:

7 or 8 drops of “liquid arsenic” in an entire Olympic sized swimming pool.

40 dimes in a stack of dimes reaching from here to the moon.

Keep drinking your water and stop worrying so much. All the stress is probably worse for cancer than a few parts per billion of arsenic. And don’t even try to switch to another water source, because in a few months someone else will threaten a class action lawsuit over elevated lead or nitrate levels in that one too.

I’m not being flippant here. I have been in this world for most of my life. I’ve spoken to and communed with (and sometimes been) every flavor of health fanatic you can imagine. I’ve worried about and researched specific ingredients and recommended that people avoid them. Some are big levers, like seed oils, excess sugar and refined grains, regular exercise, good sleep, that are worth thinking about. Others are small potatoes. Over the years, I’ve realized that hitting the big levers and focusing on living is the real path to health. You can get lost in minutiae and before you know it, your life is half gone.

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