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Water quality standards, criteria and guidelines represent "acceptable" concentrations in water, as determined by government agencies for various purposes. These numerical criteria or treatment techniques are used to monitor water quality. Though most are not legally binding, they are often used to guide regulatory actions. Broadly speaking, water quality criteria are divided into human, aquatic life and agricultural categories. Within the human health category, special attention is placed on drinking water because it is a source of direct exposure to contaminant chemicals.
About Water Quality Criteria Water quality standards, criteria and guidelines can be quite confusing because there are many different types. Generally, though not always, the word 'standard' is used to denote legally enforceable limits while criteria and guidelines are used to denote either limits that trigger some other regulatory action or are simply a suggested limit; for clarity, hereafter, we use the word 'criteria' to indicate any of these three terms. Criteria are designed to protect particular things. Therefore, the first question to ask is: "what is being protected?" in U.S. legal terms, this is known as the "beneficial use." Broadly speaking, water quality criteria are divided into human, aquatic life and agricultural categories. Within the human health category, special attention is placed on drinking water as drinking water is more closely regulated than other uses. In the U.S., the primary federal laws regulating water quality are the Safe Water Drinking Act (SWDA) which regulates public drinking water supplies and the Clean Water Act (CWA) which has the broad mission of "the restoration and maintenance of...the integrity of the Nation's waters." In addition, the States generally have water quality laws. In California the two priniciple water quality laws are the Porter-Cologne Act and Proposition 65. In Canada, drinking water guidelines are developed by the Federal-Provincial Subcommittee on Drinking Water however, actual water quality laws are the responsibility of the Provinces. Canadian aquatic life and agricultural guidelines are developed by the Canadian Council of Ministers of the Environmenet (CCME) and are not legally binding. It is important to note that very few chemicals found in water have guidelines at all. The PAN pesticide chemical database contains over 6,400 entries. The complete list of U.S. EPA primary drinking water standards contains standards for 207 chemicals or water quality characteristics, of which, just over 150 are in our pesticide database. Finally, legally binding standards almost always have a test for 'feasibility' that is, the standard is NOT set using solely health criteria but rather is set at a level that is 'economically feasible'. U.S. EPA Drinking Water Standards and Health Advisories U.S. Drinking Water Standards are set by the U.S. EPA Office of Water under the Safe Drinking Water Act (SDWA). Implementation is left to the States which can adopt standards that are more stringent. There are two categories of national drinking water standards: primary standards and secondary standards.
Health Advisories are based on non-cancer health effects for different durations of exposure (e.g., one-day, ten-day, and lifetime). They provide guidance to U.S. EPA regional offices, state governments, and other public health officials. For more on Health Advisories see the U.S. EPA Office of Water Health Advisories webpage. U.S. drinking water standards are expressed in two ways, as maximum contaminant levels (MCLs) and maximum contaminant level goals (MCLGs). Maximum Contaminant Level (MCL) The maximum contaminant level (MCL) is the highest concentration of a contaminant legally allowed in drinking water. MCLs are set as close to the maximum contaminant level goals (MCLGs) as is feasible, but may not be as stringent as the MCLG if it is technically difficult or expensive to remove the pollutant. To make this data directly comparable to other data we have converted the units from mg/L to ug/L. To convert back to mg/L simply divide by 1000. Maximum Contaminant Level Goal (MCLG) Maximum contaminant level goals (MCLGs) are non-enforceable water quality standards that, in theory, represent the highest concentration of a contaminant at which no ill effects are anticipated from consuming the water. These standards are set to create a margin of safety. In practice, there is often disagreement on where these levels should be set, and the necessary toxicology data for setting MCLGs is not yet available for many chemicals. To make this data directly comparable to other data we have converted the units from mg/L to ug/L. To convert back to mg/L simply divide by 1000. Health advisories: One-day, ten-day and lifetime Health Advisory (HA) values are maximum concentrations of a chemical in drinking water that are not expected to cause any adverse non-carcinogenic effects when consumed over the given time period. Unlike legally enforceable MCLs, health advisories are based solely on health criteria. Health advisories are not legally enforceable standards, but serve as guidance to federal, state, and local officials. U.S. EPA's definitions of these standards are as follows:
Reference dose (RfD) The reference dose (RfD) is an estimate of the amount of a given chemical a person can consume each day over a lifetime without incurring ‘appreciable risk’ of negative effects. The RfD includes a safety factor to account for human variability as well as impacts to especially sensitive population groups. To make this data directly comparable to other data we have converted the units from mg/L to ug/L. To convert back to mg/L simply divide by 1000. Drinking Water Equivalent Level (DWEL) The drinking water equivalent level (DWEL) is the concentration of a contaminant in water (in mg/L) for which no adverse, noncarcinogenic health effects are anticipated if a person is exposed over a lifetime. The formula for calculating the DWEL is: DWEL = RfD (mg/kg/day) X Body Weight (kg) / Drinking Water Consumption (L/day) The U.S. EPA makes the following assumptions when calculating DWELs:
Thus, a DWEL of 2 ug/L indicates that if the chemical concentration is less than 2 ug/Liter in drinking water, then a 70 kg adult can consume 2 liters of water each day for a lifetime without adverse effects. To make this data directly comparable to other data we have converted the units from mg/L to ug/L. To convert back to mg/L simply divide by 1000. Cancer Risk The cancer risk, sometimes called the 'excess cancer risk level' is the estimated probability that the given concentration of the contaminant in drinking water will cause 1 new case of cancer in a population of 1,000,000. This cancer risk is based on the following assumptions:
To make this data directly comparable to other data we have converted the units from a 10-4 risk level to the more common 10-6 risk level. To convert back to 10-4 risk level simply multiply by 100. We have also converted the units from mg/L to ug/L. To convert back to mg/L simply divide by 1000. About the Data: Accuracy, currency, comprehensiveness and source The Drinking Water Standards and Health Advisories tables are updated on an as needed basis. In practice, updates appear to be less than annually. The current U.S. EPA report was last updated in the summer of 2002 and replaces the previous summer 2000 report. PAN last checked this data on October 6, 2002. The U.S. EPA has set water quality standards for relatively few chemicals. The PAN pesticide chemical database contains over 6,400 entries. The complete list of U.S. EPA primary standards contains standards for 207 chemicals or water quality characteristics, of which, just over 150 are in our pesticide database. References:
Canadian Drinking Water Guidelines The Canadian Drinking Water guidelines are published by the Federal-Provincial Subcommittee on Drinking Water. An introduction to this summary states: "The guidelines are intended to apply to all public and private drinking water supplies in Canada. However, because water is a provincial responsibility, compliance with the Guidelines cannot be legally enforced, except where a province or territory chooses to do so." (4) The guidelines are divided into three classes:
Maximum Acceptable Concentrations (MACs) Maximum acceptable concentrations (MACs) are the maximum concentration expected to produce no adverse effects over a lifetime of exposure. An introduction to the guidelines state "these values...are typically 10-5000 times lower than those at which any adverse effects on health have been observed during prolonged and repeated testing" (3) Note that the MACs are required to be "achievable by available water treatment methods at reasonable cost." (4). When it is determined that the MAC cannot be achieved at 'reasonable cost' or that it cannot be reliably measured by available analytical methods an Interim MAC at a less stringent level is established. To make this data directly comparable to other data we have converted the units from mg/L to ug/L. To convert back to mg/L simply divide by 1000. Interim Maximum Acceptable Concentrations (IMACs) Interim maximum acceptable concentrations (IMACs) are values that are used when acheiving the MAC is deemed to be too expensive or not possible due to available analytical methods. IMACs are therefore recognized as being less protective of public health than MACs. To make this data directly comparable to other data we have converted the units from mg/L to ug/L. To convert back to mg/L simply divide by 1000. Aesthetic Objectives (AOs) Aesthetic Objectives, sometimes termed 'organoleptic properties' include taste, odor and appearance. They are only established for chemicals where the organoleptic threshold is less than the MAC. To make this data directly comparable to other data we have converted the units from mg/L to ug/L. To convert back to mg/L simply divide by 1000. About the Data: Accuracy, currency, comprehensiveness and source The guidelines are published in summary form with detailed supporting documents. They are updated each year in the spring. PAN last checked this data on October 6, 2002. References:
U.S. National Recommended Water Quality Criteria The U.S. National Recommended Water Quality Criteria (hereafter 'NRWQ Criteria') are developed under the Federal Clean Water Act (CWA) and are distinct from drinking water criteria which are set through a different process. Though the NRWQ Criteria are not llegally binding, they are used to implement a number of environmental programs and are used extensively in setting dischage limits in National Pollutant Discharge Elimination System (NPDES) permits. NRWQ Criteria are based solely on environmental and human health effects and do not factor in economic cost concerns or technological feasibility. There are three kinds of values in the U.S. National Recommended Water Quality Criteria document:
Criteria Maximum Concentration (CMC) CMC's are estimates of the highest concentration of a pollutant an aquatic community can be be briefly exposed to without adverse effects. 'Brief' is defined as xxx, 'aquatic community' is defined to include "the vast majority of aquatic communities in the U.S." Criterion Continuous Concentration (CCC) CCC's are estimates of the highest concentration of a pollutant an aquatic community can be be continuously exposed to without adverse effects. 'Aquatic community' is defined to include "the vast majority of aquatic communities in the U.S." Human Health Risk for Consumption The Human health risk is the estimated probability that the given concentration of the contaminant in drinking water will cause 1 new case of cancer in a population of 1,000,000. Taste and Odor (Organoleptic) Criteria Taste and odor criteria are set for substances which would make water and edible aquatic life unpalatable but not toxic to humans. About the Data: Accuracy, currency, comprehensiveness and source U.S. National Recommended Water Quality Criteria includes criteria for 166 'priority toxic pollutants' and an additional 23 organoleptic (e.g. taste and odor) criteria. Published in 1999 it is currently updated every five years. Older editions of the criteria are generally known by the color of the publication, and are cited as the 'Gold Book', 'Red book' etc.
References:
Canadian Water Quality Guidelines for the Protection of Aquatic Life The Canadian Water Quality Guidelines for the Protection of Aquatic Life are continuous exposture criteria based on toxicity data for the most sensitive species of plants and animals found in Canadian waters. Guidelines “are set at such values as to protect all forms of aquatic life and all aspects of the aquatic life cycles”. The criteria are set at levels intended to protect all life stages during an indefinite exposure to water. About the Data: Accuracy, currency, comprehensiveness and source Canadian Water Quality Guidelines for the Protection of Aquatic Life includes criteria for 211 substances. It is unclear how often this data is updated. PAN last checked this data on October 9, 2002. References:
Canadian Water Quality Guidelines for the Protection of Agricultural Water Uses Canadian Water Quality Guidelines for the Protection of Agricultural Water Uses are set at levels designed to protect sensitive crop species from chemicals which might be found in irrigation water. They are based on maximum irrigation rates and are based on the most sensitive crops. Canadian Water Quality Guidelines for Livestock Water are guidelines for livestock drinking water and specifically consider toxic accumulation. About the Data: Accuracy, currency, comprehensiveness and source Canadian Water Quality Guidelines for the Protection of Agricultural Water Uses includes criteria for 149 substances. It is unclear how often this data is updated. PAN last checked this data on October 9, 2002. References:
Last updated November 6, 2002 .
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