Series: “How Do I Know What is In My Water?”

Welcome back! If you missed my first post in this series: “Does Your Tap Water Scare You?”  go here.

All municipalities are required to extensively monitor your water. Sample upon sample is collected, sent to a certified laboratory, and then tested. If results violate the EPA’s MCL (maximum containment level) then guess what happens? More samples are collect, letters are written, and the public is notified. They are required to notify you when it happens and again in the Annual Water Quality report.

The Water Quality Report is your friend. When you get, and you should always get it by July 1 of every year, don’t just glance over it. READ IT and KEEP IT! It will tell you a lot about your water and should include:

  • The source of the drinking water, be it a river, lake, groundwater aquifer or some other body of water;
  • A brief summary of the state‚ source water assessment of the susceptibility of the source water to contamination and how to get a copy of the complete assessment;
  • EPA regulations and health goals for drinking water contaminants;
  • A list of all detected contaminants and their levels;
  • Potential health effects of any contaminant detected at a level that violates EPA‚ health standard;
  • An educational statement for people with weakened immune systems about cryptosporidium and other microbial contaminants;
  • Contact information for the water system and EPA‚ Safe Drinking Water Hotline

I bolded the one line above to make sure you saw it. If the contaminant cannot be found on your report than that means detectable levels were not found of it. What does that mean exactly? Every test preformed in a lab has a MDL (minimum detection limit). That is the smallest number that your are allowed to report and maintain certainty in the accuracy of your results. These limits are tested and verified, so if the contaminant falls below this number you can rest assured that there is little to none of it in your water. Not sure you believe it? Then call your Water Department and ask them. However, with a well maintained Water Treatment Plant it is not unreasonable to find little to no contaminants in the water supply.

Now how many of you know how to read (and understand) your Water Quality Report? Do you know what all the numbers and abbreviations mean? Well this graphic from should help:

If after reading you report you still aren’t sure and want to check into it for yourself, go here to find the certified labs in your state. Make sure you use a certified laboratory, otherwise your results will not be considered valid.

One last thing, if you are interested in what kind of contaminants can be found in the water supply, what the maximum level for them is, and how they get into our water go here: EPA Drinking Water Contaminates List. Everything that you know exists (and some that you many not have realized) is on that list.

Also, if you want to learn more about the research that the EPA uses to determine MCL check out the Water Treatability Database.

Questions or Comments? Let me know what you’re thinking!


Food and Water Watch
US EPA on Water


2 thoughts on “Series: “How Do I Know What is In My Water?”

  1. Pingback: Series: “Where’s my Water coming from?” « Chemically Inclined

  2. Pingback: Series: How do they clean my water? « Chemically Inclined

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