by Gabe Ergler
MCL – Ever wonder what it is and why it’s important?
June 1, 2016
EPA, Environmental Protection Agency

How do you know you need water treatment?

bad smelling water

Glass of water with bad taste and odor needs filter

Many are surprised to discover most natural water contains “other stuff”, that there is more in the water we drink and use daily than just water.
This other stuff can be beneficial, it can be essential nutrients our bodies need. Other stuff can improve certain appealing properties such as making the water taste better. This other stuff can also be really bad for us, it can even be downright dangerous like arsenic, lead or bacteria.


Other stuff in our water can also be quite a nuisance, not dangerous but a real pain in our otherwise wonderful life.  Nuisance stuff includes hardness, iron and silica. When present they make more work and it takes more time for us to keep homes, cars and bodies clean. They also mean our clothes may be stained, gray or dingy and our tubs, showers and sinks may be stained or plastered with soap scum. They also mean we may have to spend more time money replacing appliances.

The amount of this other stuff in our water is controlled by the EPA (U.S. Environmental Protection Agency). The EPA identifies contaminants to regulate. Then it set limits for the amount of those contaminants in water provided by public water systems.

What does MCL mean?

MCL (Maximum Contaminant Level) is the limit set by the EPA. It is the maximum permissible level of a contaminant in water which is delivered to the free flowing outlet of the ultimate user of a public water system. If your water comes to you through a public water system it should meet all EPA contaminant regulations.

EPA regulated contaminants are divided into two distinct categories – Primary and Secondary. Simply stated; Primary contaminants are those that are health related such as arsenic and lead. Secondary contaminants are those that are more of nuisance like hardness or iron.

If your water comes from a private well contaminant levels are typically regulated by your state or local health department. Most often they adopt the same EPA MCL’s but are free to be more restrictive.

A contaminant’s MCL is used to judge your water quality. MCL’s and other EPA regulations guide water treatment professionals. Test results from your water are compared against the MCL’s for each contaminant tested. If a regulated or primary contaminant is found in your water at a level higher than the EPA limit a corrective action (treatment) is prescribed to bring the contaminant level below the limit – to a acceptable level.

Well water can change over time and so it is recommended you have your water quality tested on a regular basis. Regular testing is how you will find and correct any problems. Many state and local health departments require well water testing at the time of sale of a property.  Any problems found when comparing results to the MCL are required to be addressed prior to transfer of title.

Click Here for links to EPA Primary and Secondary drinking water standards.


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