Water, water, water
At the suggestion of Scicurious, a bunch of us at Scientopia have decided to take a closer look at the science - both good and bad - behind the articles in the latest issue of Women's Health magazine. Be sure to check out the Scientopia front page where you can find all the Women's Health review posts
We're suffering from a heat wave here in Southern California. Today the temperature is expected to hit triple digits by mid-afternoon, while the relative humidity is expected to drop to a dry 10%. Dehydration is a serious concern, especially for people who have to spend time outside during the hottest part of the day. It's a lifesaver that clean water is as close as the nearest faucet.
That brings me to the article1 in Women's Health that asks "Think that's clean water coming out of your faucet?" The answer, of course, is that there are a "host of nasties" we should be concerned about. It lists four pollutants that may be found in your tap water: chlorine, lead, bacteria, and hormone and drug by-products, that has a take-home message that we should be very concerned about the toxins in the water we drink.
So should we avoid drinking water from the faucet? or is it scare-mongering? While there are indeed legitimate concerns about the safety of the water supply, I'd say the short piece makes it sound as if contaminated tap water is a much greater problem than it really is.
Water Treatment Cycle (click for details)
There is no one single source of tap water in the United States2. There are more than 150,000 public water systems in the US, supplying drinking water to the vast majority of Americans. The quality of the water varies depending on the source and the efficiency of local water treatment. But even so, the public drinking water supply is required to meet the safety standards overseen by the Environmental Protection Agency.
So what do we actually know about the "nasties" in our water supply? Read on.
In 1908 Jersey City, New Jersey became the first municipal water system in the United States to disinfect its water supply with chlorine. The treatment is very effective at killing bacteria, viruses, and parasites. Today, a century later, disinfection of drinking water has virtually eliminated water-borne diseases like cholera and typhoid fever in the U.S.
The problem is that in addition to killing pathogens, chlorine can chemically react with organic compounds in the water, creating toxic by-products, particularly trihalomethanes (THM). Those are the the "nasties" that the article refers to:
But studies show that long-term exposure to chlorine by-products can lead to miscarriage or birth defects, says Gina Solomon, M.D., a senior scientist at the Natural Resources Defense Council.
That's scary! But how great is the actual risk?
A search of the recent medical literature turns up some studies that found a relationship between exposure to chlorination by-products and birth defects, and others not so much. A recent review of the literature found that isn't enough evidence to conclude that the by-products create a significant risk of birth defects. A different review, looking at a slightly different set of studies did find a moderate association between chlorination by-products and miscarriages, particularly in women who drink five or more glasses of tap water per day.
So there may be a small risk of drinking tap water during pregnancy. Fortunately, many public water suppliers have begun to use chloramine, rather than chlorine, as a disinfectant. That reduces the total level of disinfection by-products, which is step in the right direction.
You can also help remove the contaminants yourself. Most of the chlorination by-products are volatile, meaning that they will eventually evaporate. The Women's Health article suggests letting the water stand 5 minutes before drinking, but that doesn't seem like nearly long enough to make a difference. The World Health Organization suggests boiling for 5 minutes to remove THM. You'd probably have to let the water stand at room temperature for several hours to have the same effect.
And if you are seriously concerned, don't forget that showering, bathing and swimming in chlorinated pools likely also contribute to trihalomethane exposure.
Nieuwenhuijsen MJ et al. Chlorination Disinfection By-Products in Drinking Water and Congenital Anomalies: Review and Meta-Analysis. Environ Health Perspect. 2009 October; 117(10): 1486–1493. doi: 10.1289/ehp.0900677.
Bove F. et al. Drinking water contaminants and adverse pregnancy outcomes: a review. Environ Health Perspect. 2002 February; 110(Suppl 1): 61–74. (full text)
Environmental Protection Agency: Basic Information about Disinfection Byproducts in Drinking Water: Total Trihalomethanes, Haloacetic Acids, Bromate, and Chlorite
World Health Organization: Trihalomethanes in drinking-water (pdf).
Scanning electron micrograph of E. coli.
Treatment of water with chlorine or other disinfectants kills the microbes that can make you sick. But sometimes water isn't adequately treated and pathogens can end up in your drinking water. Or as Women's Health put it:
Gnarly bacteria like E. coli can make their way into water from human and animal waste that runs into reservoirs from broken pipes and sewage systems.
E.coli infection is spread through ingestion of poop from infected animals or humans, and it can indeed be spread through drinking contaminated water, as well as eating contaminated or by contact with infected individuals. However, it's rare that it finds its way into the water coming out of your tap. Let's look at some numbers.
According to the CDC, in 2005 and 2006 there were a total of 20 disease outbreaks associated with drinking water in the U.S., affecting 612 people. To put that into perspective, that is about 300 people affected by drinking water-associated disease outbreaks per year out of a total U.S. population of roughly 300 million. Even factoring in the likelihood that some small outbreaks went unreported, such outbreaks are rare.
Twelve of those twenty outbreaks - affecting 135 people - were associated with bacterial contamination. Ten were caused by Legionella in contaminated building plumbing systems; one outbreak was caused by Campylobacter, and a single outbreak was caused by pathogenic E. coli. The E.coli outbreak affected 60 people at a camp in Oregon that was supplied with inadequately chlorinated river water.
It looks to me that as long as your local water treatment facility is functioning properly, the risk of infection from drinking tap water is extremely low.
Of course for someone who has a compromised immune system or is otherwise vulnerable to infection, even a small risk can pose a danger. Fortunately there is an easy solution: boiling water before drinking it should kill any microbes lurking within.
CDC Morbidity and Mortality Weekly Report Surveillance Summary: Surveillance for Waterborne Disease and Outbreaks Associated with Drinking Water and Water not Intended for Drinking --- United States, 2005--2006 (pdf version)
Tomorrow: Lead and pharmaceuticals.
1. It's actually not so much an article as a "List Tool", that breaks down a topic into 4 or 6 or 8 pithy points.
2. Women's Health is a U.S. magazine, so I'm assuming they are referring to the U.S. water supply.