Guide to National Primary & Secondary Drinking Water Regulations

The United States EPA (environmental protection agency) has made a lot of progress in improving drinking water quality and enforcing standards that local facilities and businesses have to adhere to.

These standards are based on research that shows the possible adverse health effects from large amounts of certain contaminants. 

In this guide, we will review the basic standards that the government requires treatment plants and other facilities to adhere to for the public water. 

Keep in mind that these are just the basic government standards and often additional filtration after receiving water from a treatment plant may be needed for the most optimal water quality.

Safe Drinking Water Act (SDWA)

The main law that governs drinking water safety in the United States is the SDWA.

The SDWA requires the US Environmental Protection Agency to enforce primary national drinking water standards that are necessary to protect the public health in public water systems. 

This law also allows the delegation of primary enforcement responsibility to states that adopt drinking water rules that are at least as strict as the national regulations

This means that as long as states meet the minimum national regulations, they can enforce their own rules.

safe drinking water act sign

National Primary Drinking Water Standards (Legally Enforceable)

The national primary drinking water standards are the basic legally enforceable standards that all plants must adhere to.

These standards protect drinking water quality by limiting the amount of specific contaminants that are known to adversely affect human health.

Below are the contaminant levels that this standard enforces.


MCL or Maximum Contaminants Level

The main level that water quality must stay below is called the Maximum Contaminants Level or MCL.

The Maximum Contaminant Level is the maximum amount of the regulated contaminant which is legally allowed to transport to the consumer’s tap water.

MCLs are enforced at public water systems and penalties are defined in the Safe Drinking Water Act if the levels are not kept in check.

MCLG or Maximum Contaminant Level Goals

Besides specifying the MCLs the USEPA also sets a Maximum Contaminant Level Goal or MCLG.

The MCLG is not legally enforceable but it sets a limit to where no known adverse effects on the health of people occur and which allows an adequate margin of safety.

The legally enforceable MCL is set as close as possible to the MCLG (since ideally if the water meets the goal criteria it would be even better) taking into consideration the costs and treatment technologies available to public water systems.

Often, to get the highest quality water that meets the MCLG or better it is necessary to install a point of use under sink or point of entry whole home filter system alongside standard water treatment plants.

The bottom line is the MCL is the legally enforceable maximum level for regulated contaminants to keep people healthy and the MCLG is the most optimal level that causes zero harm to humans which it’s best to shoot for.

Primary Drinking Water Regulations MCL and MCLG Table

Below is the table for disinfection byproducts from the EPA to give you an example of the maximum allowed contaminant in the water supply.

To see all the tables and allowable contaminants from the EPA, click here

Disinfection Byproducts

ContaminantMCLG (mg/L)MCL or TT (mg/L)
Haloacetic acidsn/a0.060
Total Trihalomethanesn/a0.080

Secondary Standards (Aesthetic)

The USEPA also issues secondary standards which are just for aesthetic, cosmetic, taste, odor, and color issues with the water supply.

These regulations are not enforceable by the federal government and intended to be used as guidelines that the states should meet anyway.

You can learn more about the secondary standards at the EPA page here

Local Water Regulations

Lastly, depending on where you live there may be different maximum contaminant levels based on your local government.

Remember that as long as the states meet the primary drinking water regulations for contaminants they can set their own rules after.

To find out about your local drinking water regulations search for your local water treatment plant and look for their regulatory rules.


Concluding Thoughts

Now you have a better idea of the main drinking water regulations in the United States and what levels of contaminants are allowed in the tap water.

The Safe Drinking Water Act of 1974 was a big step forward in ensuring that all people have access to clean drinking water but you should still keep in mind that the treatment facilities are only regulated on the maximum contaminant level standard and they often do not meet the highest quality standards.

In order to ensure your tap water meets the maximum contaminant level goal or better and your water is as pure and healthy as possible it often makes sense to invest in a home water filtration system.