What’s in Your Water?

by Bill Chameides | May 25th, 2010
posted by Erica Rowell (Editor)

Permalink | 3 comments

Water, water everywhere, but how much — and by whose standards — is safe to drink?

The U.S. Geological Survey (USGS) has been mucking around in wells. Surprise: it’s not all muck.

About 105 million Americans — or around one-third of the nation — rely on some 140,000 public wells for their drinking water. The USGS’s latest installment on the state of our drinking water sheds some light on the quality of that water. Is it good news or bad news? Judge for yourself.

First some quick stats. The study covered:

  • 30 aquifers,
  • 41 states,
  • 932 public wells, and
  • less than one percent of U.S. groundwater-supplied public water systems.

Water: Untreated vs. Treated-and-Unhealthy

Percentage of untreated water samples that had at least one contaminant at levels designated by
the USGS to be of potential health concern*: > 20

This means that the chemicals we use in our agriculture, industry and homes aren’t just making their way into surface waters; they are also finding their way into the groundwater that finds its way into our drinking water supply.

Fortunately, very few of us drink water straight out of the ground. All public water supplies are treated to some extent before consumption. And so most people should be greatly relieved by the following statistic.

Percentage of treated water samples found to have at least one contaminant at levels designated by the
USGS to be of potential health concern
: 0 (source)

Unfortunately, a companion study of private drinking water also found that more than 20 percent of private domestic wells sampled contained at least one contaminant at levels of potential health concern. The important difference being that water from private wells does not undergo additional treatment.

Water: Untreated vs. Treated-and-Officially-Not-Unhealthy

I imagine some people may prefer not drinking contaminated water even if it meets health standards. If so, those folks would no doubt find these next statistics of interest.

Percentage of untreated water samples that had at least two contaminants present but not necessarily
at levels of potential health concern: 70 (source)

Percentage of treated water samples that had at least two contaminants present but not necessarily at levels
of potential health concern: 82 (source)

Note anything strange here? Treated water has more contaminants than untreated water. How come? Two reasons. Most treatment processes are simply designed to disinfect the water. This means that the treatment:

  1. is often ineffective against some types of contaminants, allowing them to pass through to the finished water, and
  2. can add byproducts of the disinfectant process to the finished water.

Regulated vs. Unregulated Water Supplies

Number of contaminants identified in USGS study: 337 (source)

Number of contaminants identified that are regulated by the Environmental Protection Agency via the Safe
Drinking Water Act: 58

Number of contaminants that are not regulated but carry USGS health-based concerns: 135

Number of contaminants identified that are neither regulated nor have a USGS Health-Based Screening Level*
(largely because of a lack of data): 144

Bottled Water Vs. Tap Water: Not Much of a Contest There

If all this makes you so concerned that you want to swear off tap water and go on a steady diet of bottled water, that might not be such a good idea.

Consider that Peter Gleick, fellow member of the National Academy of Sciences and author of Bottled and Sold: The Story Behind Our Obsession With Bottled Water, found that 40 percent of the bottled stuff is from reprocessed municipal water. And for the other half or so that doesn’t come from public water supplies? Well, in general, municipal water supplies are much more tightly regulated and monitored than bottled water products (see table below). And, given the paucity of data on bottled water, it’s a safe bet that you’re better off with tap water even if it means we should still take steps to ensure its safety.

Tighter regulations surrounding tap water means it’s probably overall safer than the bottled stuff.

For More Information



*A contaminant is of potential health concern when either the maximum contaminant level of the Safe Drinking Water Act or the USGS’s Health-Based Screening Level (HBSL) developed in concert with EPA and other agencies is exceeded.

The HBSL is a measure of contaminant levels in water that, if exceeded, may be of potential concern for human health. It is a not a regulatory level, but instead is designed to give preliminary information on the potential impacts of compounds in our water.

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  1. dave
    May 26, 2010

    Excellent Message Bill DalaiLama Tweets; If we are truly concerned about the environment, we must think not only for this generation, but for future generations as well. My tweet: Officially WASTE WATER Month: metered water owners oppose:( The rest of us should turn ON Taps; let the Water go Free

  2. MattN
    May 25, 2010

    What the percentages were back in the 1950s and 60s. I have a continual argument with another online personality that we are, bar far, better stewards of the environment in 2010 than we ever thought of being in, say, 1970. I hold the Tukaseegee river flowing through Bryson City, NC as Exhibit A. I clearly remember in the ’70s white foam floating down the river filled with black rocks stained from the raw discharge of an upstream paper mill in Sylva. I wanted to swim in it, I was forbidden (what did I know, I was 6yo). I wanted to go fishing in it, but was told no fish lived in it. Now, it is a state hatchery supported trout stream that people go tubing and kayaking on. The cars I remember lining the banks (for erosion?) have been removed. Its really a beautiful river, now that we aren’t using as an open air sewer. So, are we getting better or worse? I don’t know the answer, but if I were a betting man, I’d bet those numbers are better (perhaps significantly) than they were 40-50 years ago.

    • Bill Chameides
      Jun 7, 2010

      MattN: I suspect that you are absolutely right. Since the passage of the Clean Water Act in the ‘70s, water quality in the United States has improved dramatically. That is testament to the importance of federal regulation to protect the public welfare when it comes to the environment — I’m glad we can at least agree about that. But even so, that doesn’t mean there are not still problems with our water quality. The chemical cocktail in our waters is changing from a more visible one (like what you describe) to one that is less visible but possibly dangerous. And the statistics included in the post point to positives but also some areas for concern. We are fortunate to have programs like that of the USGS to carry out national water quality assessments. The data from those assessment are mixed. For example, water quality in the Southeast from 1973-2005 has both increasing and decreasing trends depending on the parameter and location.

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