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Water: Basic Information about Regulated Drinking Water Contaminants

Basic Information about Diquat in Drinking Water

Diquat at a Glance

Maximum Contaminant Level (MCL) = 0.02 milligrams per liter (mg/L) or 20 parts per billion (ppb)

Maximum Contaminant Level Goal (MCLG) = 0.02 mg/L or 20 ppb

Health Effects
Some people who drink water containing diquat in excess of the MCL over many years could get cataracts.

Drinking Water Health Advisories provide more information on health effects

Chemical Abstract Service Registry Number
85-00-7

Sources of Contamination
Runoff from herbicide use

List of all Regulated Contaminants (PDF) (6 pp, 396K, About PDF)

EPA regulates diquat in drinking water to protect public health. Diquat may cause health problems if present in public or private water supplies in amounts greater than the drinking water standard set by EPA.

What is diquat?
Diquat is an organic solid of colorless or yellow crystals. A water solution is dark red-brown.

Uses for diquat.
Diquat is a herbicide that has been used extensively in the United States since the late 1950s to control both cropand aquatic weeds. It is used on potatoes; as an aid in harvesting cotton, rapeseed and other oil seed crops; to wilt and dry out silage, standing hay, etc., for storage; a plant growth regulator and sugar cane-flowering suppressant.

If you are concerned about diquat in a private well, please visit:

What are diquat's health effects?
Some people who drink water containing diquat well in excess of the maximum contaminant level (MCL) for many years could get cataracts.

This health effects language is not intended to catalog all possible health effects for diquat. Rather, it is intended to inform consumers of some of the possible health effects associated with diquat in drinking water when the rule was finalized.

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What are EPA's drinking water regulations for diquat?
In 1974, Congress passed the Safe Drinking Water Act. This law requires EPA to determine the level of contaminants in drinking water at which no adverse health effects are likely to occur. These non-enforceable health goals, based solely on possible health risks and exposure over a lifetime with an adequate margin of safety, are called maximum contaminant level goals (MCLG). Contaminants are any physical, chemical, biological or radiological substances or matter in water.

The MCLG for diquat is 0.02 mg/L or 20 ppb. EPA has set this level of protection based on the best available science to prevent potential health problems. EPA has set an enforceable regulation for diquat, called a maximum contaminant level (MCL), at 0.02 mg/L or 20 ppb. MCLs are set as close to the health goals as possible, considering cost, benefits and the ability of public water systems to detect and remove contaminants using suitable treatment technologies. In this case, the MCL equals the MCLG, because analytical methods or treatment technology do not pose any limitation.

The Phase V Rule, the regulation for diquat, became effective in 1994. The Safe Drinking Water Act requires EPA to periodically review the national primary drinking water regulation for each contaminant and revise the regulation, if appropriate. EPA reviewed diquat as part of the Six Year Review and determined that the 0.02 mg/L or 20 ppb MCLG and 0.02 mg/L or 20 ppb MCL for diquat are still protective of human health.

States may set more stringent drinking water MCLGs and MCLs for diquat than EPA.

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How does diquat get into my drinking water?
The major source of diquat in drinking water is runoff from herbicide use.

A federal law called the Emergency Planning and Community Right to Know Act (EPCRA) requires facilities in certain industries, which manufacture, process, or use significant amounts of toxic chemicals, to report annually on their releases of these chemicals. For more information on the uses and releases of chemicals in your state, contact the Community Right-to-Know Hotline: (800) 424-9346.

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How will I know if diquat is in my drinking water?
When routine monitoring indicates that diquat levels are above the MCL, your water supplier must take steps to reduce the amount of diquat so that it is below that level. Water suppliers must notify their customers as soon as practical, but no later than 30 days after the system learns of the violation. Additional actions, such as providing alternative drinking water supplies, may be required to prevent serious risks to public health.

If your water comes from a household well, check with your health department or local water systems that use ground water for information on contaminants of concern in your area.

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How will diquat be removed from my drinking water?
The following treatment method(s) have proven to be effective for removing diquat to below 0.02 mg/L or 20 ppb: granular activated carbon.

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How do I learn more about my drinking water?

EPA strongly encourages people to learn more about their drinking water, and to support local efforts to protect the supply of safe drinking water and upgrade the community water system. Your water bill or telephone book's government listings are a good starting point for local information.

Contact your water utility. EPA requires all community water systems to prepare and deliver an annual consumer confidence report (CCR) (sometimes called a water quality report) for their customers by July 1 of each year. If your water provider is not a community water system, or if you have a private water supply, request a copy from a nearby community water system.

Other EPA Web sites

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