Maximum contaminant level (MCL)
The highest level of a contaminant that the EPA allows in public drinking water systems. The EPA sets MCLs at levels that are economically and technologically feasible.
- Arsenic: 10 micrograms per liter (µg/L)
- Nitrate: 10 milligrams per liter (mg/L)
- Radium: 5 picocuries per liter (pCi/L)
- Uranium: 15 picocuries per liter (pCi/L)
- TTHM: 80 micrograms per liter (µg/L)
- HAA5: 60 micrograms per liter (µg/L)
The limit of detection is the smallest amount of a chemical that a laboratory method can reliably distinguish from zero. Measurements below this limit are reported as non-detects (ND)
Some systems have treatment in place to address contaminants. There may be a temporary spike in results due to any treatment failures. These contaminants are monitored regularly and any treatment failures are identified immediately and addressed.
Public Water Systems may have added treatment or removed a source, so the most recent data results should be the most accurate
'Principal County Served' as per Public Water System's primary mailing address
In February 2016, MDH noticed that drinking water samples were not cooled consistently during shipping to the Lab. Temperature control is necessary for proper analysis of organic materials, such as haloacetic acids and trihalomethanes. In most cases, analysis results are likely to be very similar from samples that were properly cooled (arriving at the lab at less than or equal to 6 degrees C). Cooling during shipment delays or stops contaminant degradation. Lab results were likely lower than when the water was collected.
MDH revised its sample handling procedures by March 1, 2016. Analysis results for organic materials from dates after March 1, 2016 have greater confidence levels. Annual results represent an average of the test results within a year. Non-detect (ND) values are set to ½ the detection limit as determined by the public health lab. If all results within a year are non-detect values, the mean and maximum values are labeled with ND. Not all systems are tested every year for each contaminant. Results are carried forward for years with no testing.