I have nonallergic rhinitis. I have had great success keeping it under control with 10 milligrams of Cetirizine (one brand is Zyrtec) every night and using a neti pot to wash out my nasal passages twice a day, night and morning. My neti pot ritual has been pretty simple: use the little spoon provided with certain brands of neti pots to measure out and stir non-iodized salt into warm tap water. (Iodized salt burns and isn’t a good idea.) Then tip my head and pour the salted water into one nose and out the other. Blow my nose as needed—which is a lot. Reverse directions and repeat. Stop when the water is gone. Then I’m done.
But with the latest report of a woman dying from a freshwater amoeba infection (see above), I am being urged by those close to me, as well as by authorities to use only distilled or boiled water instead of tap water. (Of course, the boiled water needs to be allowed to cool before use!)
I’m not the only one using a neti pot and having to think about whether it is worth the trouble to use distilled or boiled water. Neti pots became fairly popular after Oprah touted them. On that, see “Yahoo! Reveals Oprah’s Effect on Web Searches” and the academic article below:
Let me approach my decision using the tools of cost-benefit analysis. Over a number of years’ time, there have been 4 widely publicized reports of brain-eating amoebae cases in the United States attributed to neti pot use by doctors. There are two types of brain-eating amoebae that have been blamed: Naegleria fowleri and now Balamuthia mandrillaris. (Technically, Naegleria fowleri is a “shapeshifting amoeboflagellate excavata,” not an amoeba.) Wikipedia currently says that Naegleria fowleri “is typically found in bodies of warm freshwater, such as ponds, lakes, rivers, and hot springs.” Balamuthia mandrillaris “is believed to be distributed throughout the temperate regions of the world” in the soil and water.
In order to get a number for the annual risk of neti-pot use with salted tap water, I need to guess number of people using neti pots with salted tap water, the number of brain-eating amoeba cases per year due to neti pots, and the fraction of those brain-eating amoeba cases from neti pot use that are due to people using unsalted tap water. This distinction matters because, salt might kill or weaken freshwater amoebae. From “Is My Neti Pot Going to Kill Me?” shown above:
It’s not just about avoiding irritation, either—achieving the proper salinity protects you from microorganisms that can’t survive in saltwater, like Naegleria fowleri. “It's a freshwater thing,” says Iaquinta.
Brain-eating amoeba cases due to neti pot usage are sensational news, so let me assume that most such cases are well-reported. To lean on the high side, let’s suppose there are on average 3.25 such cases per year in the US. Unfortunately, I can’t find any numbers on neti-pot usage by googling around. And the number of people who use tap water instead of distilled water will be even harder to find out. (I’d be glad for help!) Let me suppose that 1% of the US population is using neti pots with tap water. That is about 3.25 million people. And since doing neti pot without using salt is very unpleasant (I’ve made the mistake a few times), let me simplify by imagining that all neti pot users put salt in. That last assumption makes the risk estimate higher than it would otherwise be. One last assumption that makes the incremental risk estimate higher than it otherwise be is to assume that someone who uses a neti pot with distilled or boiled water faces no risk. Putting all of that together gets me to a literal one-in-a-million risk annually. And you can see how changing the assumptions would change the incremental risk estimate.
How bad is a one-in-a-million annual risk? Economists use a concept called “the value of a statistical life” to turn such a tiny risk into dollars. $10 million is a relatively high number for the value of a statistical life. (See various estimates down at the bottom of the Wikipedia article “Value of life.”) A one-in-a-million annual chance of a $10 million hit is a cost of $10 per year. Think of that $10 million value of a statistical life as applying to someone with a US median level of income. Then whether someone at the median level of income should take the trouble to use distilled or boiled water should depend on whether they assess the time, money and trouble of using distilled or boiled water as more or less than the $10 per year cost from brain-eating amoeba risk of not using distilled or boiled water. I suspect that most people at a US median income would judge the time, money and trouble cost of using distilled or boiled water instead of tap water to be greater than $10 a year. So it is a reasonable decision to use tap water (with salt, of course, since it is very unpleasant not to use salt). Note that since the risk is entirely to oneself, some of the ethical concerns with using the value of a statistical life for cost-benefit analysis that show up in contexts where one is making a decision for others are muted in this context.
Getting the cost-benefit calculations right is important not only because many people may be making unwarranted expenditures of money, time and trouble, but also because some people who could benefit from using a neti pot may be discouraged from doing so because they think they have to used distilled or boiled water.
Those who are above the median income could reasonably think that they can afford to pay more for probabilities of their own survival at more than $10 million for a life (= $100,000 for each 1% chance). But the time and trouble costs of using distilled or boiled water would also be higher for those at higher incomes who also have higher hourly wages or a higher hourly dollar valuation of time for any other reason. Theoretically, if the marginal utility of a dollar declines faster than 1% for every 1% increase in consumption (as I believe it does), then the value of a statistical life should go up more-than-proportionately with the level of consumption. (The total util value of a life should go up some with a higher level of consumption; and likely much more importantly quantitatively, one then converts utils into dollars using the reciprocal of the marginal utility of consumption.) On average, a more-than-proportionate increase in the value of a statistical life with the level of consumption should make the dollar value of a statistical life go up faster with income than the value of time. And some of the cost of using boiled or distilled water is a cost in money. So among neti-pot users, if people are somewhat rational, I would expect more high-income folks to go to the trouble of using boiled or distilled water than moderate-income folks. (A tendency toward following the average practice within a society would reduce this effect, but shouldn’t eliminate it.) The ultra-rich who also have ultra-high levels of consumption could have their employees take on almost all of the extra time and trouble cost of using distilled or boiled water instead of tap water, and so should probably use boiled or distilled water.
All of that makes it a nonobvious decision for me, personally, whether to go to the trouble of using boiled or distilled water. It all depends on how easy and fast the procedure can be made when using boiled or distilled water. But what is obvious is that I shouldn’t stress myself out about this decision. It’s not a big deal either way. (On the costs of decision-making, see “Cognitive Economics.”)
Let me note that doing the cost-benefit analysis I sketch out above more carefully would be a great senior-thesis project of an undergraduate in economics. But it would take some legwork.
For annotated links to other posts on diet and health, see: