Chemical Contaminant Rules

On this page:

• Rule Summary
• Rule History
• Compliance

Rule Summary

The chemical contaminants were promulgated in phases collectively called the Phase II/V Rules or the Chemical Contaminant Rules. These rules regulate over 65 contaminants in three contaminant groups:

• Inorganic Contaminants (IOCs) (including nitrate and arsenic),
• Volatile  Organic Contaminants (VOCs), and
• Synthetic Organic Contaminants (SOCs).

In 2001, EPA adopted a lower standard for arsenic in drinking water that applies to both community water systems and non-transient non-community water systems. The new arsenic standard of 10 parts per billion (ppb) replaces the old standard of 50 ppb. Several useful reference materials are provided below:

• The Technical Fact Sheet: Final Rule for Arsenic in Drinking Water contains requirements and compliance dates, the health effects associated with exposure to arsenic, the costs, benefits, and number of systems affected by the rule.
  Read the Arsenic Rule Technical Fact Sheet (PDF)(6 pp, 347 K, About PDF) EPA 815-F-00-016, January 2001
• The Drinking Water Standard for Arsenic Fact Sheet provides information on the potential health effects from exposure to arsenic, an overview of the Final Rule, and background information on the natural occurrence of arsenic.
  Read the Drinking Water Standard for Arsenic Fact Sheet (PDF)(2 pp, 140 K, About PDF) EPA 815-F-00-015, January 2001

Rule History

Background Information on the Chemical Contaminant Rules

The chemical contaminants were promulgated in phases collectively called the Phase II/V Rules or the Chemical Contaminant Rules. These rules regulate over 65 contaminants in three contaminant groups:

• Inorganic Contaminants (IOCs) (including arsenic and nitrate),
• Volatile Organic Contaminants (VOCs), and
• Synthetic Organic Contaminants (SOCs).

The rules apply to all public water systems (PWS). PWS type, size, and water source type determine which contaminants require monitoring for that system.  

Over a five year period, EPA gathered and analyzed occurrence and health effects data. Through the Phase II/V Rules, EPA established:

• Maximum Contaminant Level Goals (MCLGs),
• Maximum Contaminant Levels (MCLs),
• Monitoring requirements, and
• Best available technologies for removal for 65 chemical contaminants.

The Chemical Contaminants Rules provide public health protection through the reduction of chronic, or long-term, risks from:

• Cancer,
• Organ damage,
• Circulatory system disorders,
• Nervous system disorders, and
• Reproductive system disorders.

There is an acute health risk from nitrate and nitrite. The regulations reduce the risk of Methemoglobinemia or "blue baby syndrome." Blue Baby Syndrome is caused from ingestion of high levels of nitrate or nitrite.

Regulated Chemical Contaminants

EPA set a Maximum Contaminant Level Goal (MCLG) for each contaminant. The MCLG is the maximum level of a contaminant in drinking water at which no known or anticipated adverse effect on the health of persons would occur, and which allows an adequate margin of safety. MCLGs are not enforceable. 

The MCLG is not a legal limit set for PWSs. It is based solely on human health. For known cancer-causing contaminants the MCLG is set at zero. This is because any chemical exposure could present a cancer risk.

The Chemical Contaminants Rules also set Maximum Contaminant Level (MCL) for each contaminant. EPA sets MCLs as close to the health goal as possible. The MCL weighs the technical and financial barriers with public health protection.

The following link is a table of all regulated drinking water contaminants:

• Contaminants with established MCLs and MCLGs

The following table details the VOCs, SOCs, and IOCs that are regulated in each phase of the Phase II/V Rules.

¹Aldicarb, aldicarb sulfone, and aldicarb sulfoxide are considered regulated chemicals. However their MCLs are stayed and no monitoring is required (57 FR 22178, May 27, 1992).

² The MCL for nickel was remanded in 1995 but PWSs are still required to monitor.

Background Information on Arsenic

Arsenic is one of the inorganic contaminants regulated under the Phase II/V Rules. In 2001, under the Arsenic Rule, EPA adopted a lower standard for arsenic in drinking water. The lower standard of 10 parts per billion (ppb) replaced the prior standard of 50 ppb.

Arsenic is a semi-metal element in the periodic table. It is odorless and tasteless. It can enter drinking water supplies from natural deposits in the earth or from agricultural and industrial practices. 

Non-cancer effects of arsenic can include:

• Thickening and discoloration of the skin,
• Stomach pain,
• Nausea,
• Vomiting,
• Diarrhea,
• Numbness in hands and feet,
• Partial paralysis, and
• Blindness.

Arsenic has been linked to a number of cancers. These include cancer of the bladder, lungs, skin, kidney, nasal passages, liver, and prostate.

EPA set the arsenic standard for drinking water at 10 ppb (or 0.010 parts per million). This protects consumers from the effects of long-term, chronic exposure to arsenic. PWSs had to comply with the lower standard by January 23, 2006.

Background Information on Nitrate and Nitrite

Nitrate and Nitrite are the only acute inorganic contaminants regulated under the Phase II/V Rules. The greatest use of nitrates is as a fertilizer.

Nitrates and nitrites are nitrogen-oxygen chemical units which combines with various organic and inorganic compounds. Once taken into the body, nitrates are converted into nitrites. High levels of nitrate and nitrite are most serious for infants.

The conversion of nitrate to nitrite by the body, can interfere with the oxygen-carrying capacity of the child’s blood, sometimes called Blue Baby Syndrome. This acute condition can occur rapidly over a period of days. Symptoms include shortness of breath and blueness of the skin.

The standard for Nitrate is 10 mg/L or ppm and for Nitrite it is 1 mg/L or ppm.

For more information, including federal register notices, use the links below:

• Chemical Contaminant: Phase II/V Rule Regulatory History
• Phase II/V Rule Regulatory Corrections and Significant Rule Developments
• Phase II/V Rules in the Code of Federal Regulations
• Arsenic Rule History

Compliance

Compliance is key to public health protection.  EPA and the state and tribal primacy agencies help to support compliance monitoring in public water systems.  The following provide support for compliance assistance to both the co-regulators and the regulated community water systems:

• Chemical Contaminant Rule Compliance for Primacy Agencies
• Chemical Contaminant Rule Compliance for Community Water System Owners and Operators
• Arsenic Rule Compliance for Primacy Agencies
• Arsenic Rule Compliance for Community Water System Owners and Operators