Guidance Values and Standards for Contaminants in Drinking Water
On this page:
- Drinking Water Standards and Guidance
- Is Water Safe to Drink if Contaminant Levels Exceed Standards or Guidance?
- Contaminants in Drinking Water
- MDH’s Role in Protecting Water Quality
- Partners in Safe Drinking Water
Drinking Water Standards and Guidance
Minnesota Department of Health (MDH) uses and develops different types of guidance for different purposes to protect people’s health from contaminants in drinking water. Drinking water that is contaminated above the standard or guidance may pose some level of health risk to some people drinking the water.To see state guidance and/or federal standards for contaminants in drinking water:
Maximum Contaminant Levels (MCLs)
Maximum Contaminant Levels (MCLs) are set by the United States Environmental Protection Agency (US EPA) and enforced by MDH. All public water supplies in Minnesota must meet these standards.
MCLs are established through a scientific process that evaluates the health impacts of the contaminant and the technology and cost required for prevention, monitoring, and/or treatment. States are allowed to enforce lower (more strict) standards than MCLs, but are not allowed to enforce higher (less strict) standards. New MCLs or changes to existing MCLs are rarely made.
Maximum Contaminant Level Goals (MCLGs)
Maximum Contaminant Level Goals (MCLGs) are established through a scientific process that only considers the health impacts of a contaminant in water. MCLGs are intended to be protective of sensitive populations like infants, children, and others who may be at increased risk of negative health impacts. MCLGs do not consider cost and technology of prevention and/or treatment and may be set at levels that are costly, challenging, or impossible for a water system to meet.
Health Advisories are established by the US EPA. Health advisories are based on non-cancer health effects for different lengths of exposure (one day, ten days, or lifetime). Health advisories provide technical guidance to the US EPA and other public health officials and are not used to regulate public water supplies.
Health-Based Values (HBVs) and Health Risk Limits (HRLs)
Health-Based Values (HBVs) and Health Risk Limits (HRLs) are developed by toxicologists at MDH using the best science and public health policies available at the time of their development. An HBV or HRL is the level of a contaminant that can be present in water and pose little or no health risk to a person drinking that water. HBVs and HRLs are developed to protect sensitive or highly exposed populations. HBVs and HRLs are guidance used by the public, risk managers, and other stakeholders to make decisions about managing the health risks of contaminants in groundwater and drinking water. HRLs are guidance values that have been through the Minnesota rulemaking process, which includes at least one public comment period for stakeholders to provide feedback on the proposed guidance values.
HBVs and HRLs are based only on potential health impacts and do not consider cost and technology of prevention and/or treatment and may be set at levels that are costly, challenging, or impossible for a water system to meet.
Risk Assessment Advice (RAAs)
Risk Assessment Advice (RAA) for water is technical guidance concerning exposures and risks to human health. RAA may be quantitative (e.g., a concentration of a chemical that is likely to pose little or no health risk to humans) or qualitative (e.g., a written description of how toxic a chemical is in comparison to a similar chemical). Generally, RAA contains greater uncertainty than HRLs and HBVs because the available information is more limited. Occasionally, MDH derives guidance as RAA not because of information limitations but because the risk assessment methodology used to derive the value is different than what is in rule.
Is Water Safe to Drink if Contaminant Levels Exceed Standards or Guidance?
Public water supplies that exceed MCLs for any contaminant must take action to reduce that contaminant in drinking water. For most people, water that meets all MCLs is safe to drink. Further action to protect health can be taken by a water supplier or citizen at levels below the MCL.
MDH develops its health-based guidance (HRLs, HBV, RAA) by considering health impacts to the most sensitive and most exposed populations across all stages of human development. For additional information see Health-Based Guidance Development Process.
HBVs, RAA, and EPA Health Advisories are developed on a more frequent basis than MCLs, MCLGs, or HRLs, and may also consider more recent information on the health risks of a contaminant. At times, an old HRL value and a newer guidance value may be available for the same chemical. For an explanation, please see Dual Guidance for Drinking Water.
Minnesota’s public water systems can use health-based guidance as goals, benchmarks, or indicators of potential concern. Some public water suppliers may strive to meet health-based guidance for contaminants for which it is possible and cost effective.
No water is completely free of contaminants. In situations where a sample of groundwater contains multiple chemicals, MDH evaluates exposure to multiple chemicals using an additivity model. For more information, see: Evaluating Concurrent Exposures to Multiple Chemicals. All Minnesotans can use the various guidance values to determine what level of a contaminant in water is acceptable for themselves and their family.
Treatment options may be available to reduce levels of contaminants in your drinking water if testing, either by you or a public water supply, shows that contaminants have been found at levels that are a concern to you.
Contaminants in Drinking Water
No water supply is ever completely free of contaminants. Drinking water standards protect Minnesotans from substances that may be harmful to their health. Some contaminants, such as arsenic and manganese, occur naturally in our environment. Other contaminants enter our water supplies as a result of our own behaviors. Fertilizer and pesticides in run off from lawns and farm fields, cleaners and personal care products that go down household drains, and industrial leaks or improper waste disposal can all lead to water contamination.
It is normal for people to want their drinking water to be completely free of all contaminants. However, preventing or removing all contamination may not be economically or technologically feasible or necessary to protect our health. US EPA and MDH are responsible for determining the levels of contaminants that can remain in water supplies without threatening human health.
MDH’s Role in Protecting Water Quality
MDH’s scientists includes a wide variety of water quality experts (hydrologists, engineers), research scientists (toxicologists, exposure scientists, epidemiologists),and public health professionals (risk assessors, risk communicators) who work together to assess the public health risks of contaminants in drinking water and monitor drinking water. MDH provides guidance and information about safe drinking water to public water suppliers and private well owners and works with other state and federal agencies, communities, non-governmental organizations, and citizens to protect and maintain Minnesota’s groundwater, rivers, and lakes that are the sources of our drinking water.
A shorter, printable version of this information is also available: Guidance Values and Standards for Contaminants in Drinking Water (PDF).
Partners in Safe Drinking Water
The US EPA, MDH, public water systems, and citizens work in partnership to keep our drinking water clean and safe for all Minnesotans.
The 1974 federal Safe Drinking Water Act directs the US EPA to set national drinking water standards for naturally occurring and man-made contaminants in public drinking water. These standards represent legally enforceable limits. MDH enforces these drinking water standards for public water supplies in Minnesota.
The 1989 Groundwater Protection Act directs MDH to develop health-based guidance values for groundwater that is used for drinking water. These values are used by state programs to protect people and the environment. These values are especially important when no other guidance value is available.
Public water systems regularly test drinking water supplies for the contaminants included in the Safe Drinking Water Act. Public water supplies must meet the drinking water standards set by the US EPA. Results of this testing are available to customers in an annual consumer confidence report.
In Minnesota, private well construction is regulated by MDH and a water test for bacteria, nitrate, and arsenic is required when a new well is constructed. After that initial test, the well owner is responsible for well maintenance and testing their drinking water.
Every Minnesotan has a role in protecting our drinking water resources. Using water wisely, preventing contamination, and planning for future needs will help provide clean, healthy water for generations of Minnesotans.