Drinking Water Standards for Regulated Contaminants

Through the Safe Drinking Water Act (SDWA), Congress requires EPA to regulate contaminants which may be health risks and which may be present in public drinking water supplies. Passed in 1974, and revised in 1986 and 1996, SDWA extends public health protection to America's drinking water consumers.

Under SDWA, EPA sets legal limits on the levels of certain contaminants in drinking water. The legal limits reflect both the level that protects human health and the level that water systems can achieve using the best available technology. Besides prescribing these legal limits, EPA rules set water-testing schedules and methods that water systems must follow. The rules also list acceptable techniques for treating contaminated water. SDWA gives individual states the opportunity to set and enforce their own drinking water standards if the standards are at least as strong as EPA's national standards. Most states and territories directly oversee the water systems within their borders.

Between 1974 and 1986, EPA regulated approximately 20 contaminants. Congress's 1986 SDWA revisions named 83 contaminants and required EPA to regulate all of them by 1989. The following six rules are EPA's response to that Congressional mandate.

To go directly to a specific rule, choose a link:
Phase I Rule
Phase II & IIb Rules
Phase V Rule
Surface Water Treatment Rule
Total Coliform Rule
Lead & Copper Rule

The Phase I, II, IIb, and V Rules

EPA regulates most chemical contaminants through the rules known as Phase I, II, IIb, and V. The Agency issued the four rules regulating 69 contaminants over a five-year period as it gathered, updated, and analyzed information on each contaminant's presence in drinking water supplies and its health effects. In each rule, EPA set limits on the contaminants, prescribed the schedule under which water systems must test for the presence of the contaminants, and described the treatments which systems may use to remove a detected contaminant. In some cases, EPA revised limits which existed prior to 1986.

For each contaminant, EPA set a health goal, or Maximum Contaminant Level Goal (MCLG). This is the level at which a person could drink two liters of water containing the contaminant every day for 70 years without suffering any ill effects. This goal is not a legal limit with which water systems must comply; it is based solely on human health. For known cancer-causing agents (carcinogens), EPA set the health goal at zero, under the assumption that any exposure to the chemical could present a cancer risk.

The rules also set a legal limit, or Maximum Contaminant Level (MCL), for each contaminant. EPA sets legal limits as close to the health goal as possible, keeping in mind the technical and financial barriers that exist. Except for contaminants regulated as carcinogens, most legal limits and health goals are the same. Even when they are less strict than the health goals, the legal limits provide substantial public health protection.

The contaminants regulated in these rules pose long-term, or chronic, health risks. Some can accumulate in the liver or kidneys and interfere with their functions. Others could affect the nervous system if ingested over a lifetime at levels consistently above the legal limit (MCL). Several of these contaminants have health goals (MCLGs) of zero because EPA believes that they cause cancer and assumes that any amount of exposure, no matter how small, poses some risk of cancer. Other contaminants present health risks only at levels above their legal limits.

Along with their long-term effects, nitrate and nitrite are also acute health risks, meaning that they could cause immediate health problems for infants, even when consumed in tiny doses. Nitrate and nitrite can limit the blood's ability to carry oxygen from the lungs to the rest of the body. EPA's limit on nitrate and nitrite in drinking water specifically protects infants.

The Phase I Rule (published 8 July 87/effective 9 January 89) was EPA's first response to the 1986 Amendments. The rule limits exposure to eight chemicals that may be present in tap water. All eight are Volatile Organic Chemicals (VOCs) that industries use in the manufacture of rubber, pesticides, deodorants, solvents, plastics, and other chemicals. The rule requires water systems to monitor and, if levels exceed legal limits, take corrective action to ensure that consumers receive water that does not contain harmful levels of the chemicals.

A 1982 survey of America's ground water supply found at least a trace of one VOC in 28 percent of large water systems (those serving more than 10,000 people) and 17 percent of small systems (those serving 10,000 people or fewer). People encounter some of these chemicals daily, in places such as the dry cleaners and automotive service stations, while others are used only in industrial processes.

When it issued the Phase II and IIb Rules (published 30 January and 1 July 1991/effective 30 July 1992 and 1 January 1993), EPA updated or created legal limits on 38 contaminants. Some of these contaminants are frequently-applied agricultural chemicals (nitrate is often present in areas where farmers apply fertilizer) while others are more obscure industrial intermediates (trans-1,2-Dichloroethylene is a solvent and chemical used in the production of other chemicals).

For 36 of the 38 contaminants that the Phase II and IIb rules address, EPA set both health goals and legal limits. The other two contaminants that EPA regulated through the rules, Acrylamide and Epichlorohydrin, are chemicals that some water systems add during the water treatment process. Known as flocculants, these chemicals bond with dirt and other tiny contaminants in water and drag them to the bottom of the treatment tank. Water systems then use the cleaner water from the top of the tank. The rules limit the amount of these chemicals that systems may add to water during the treatment process.

The Phase V Rule (published 17 July 1992/effective 17 January 1994) set standards for 23 more contaminants. Several are inorganic chemicals such as cyanide that are present naturally in some water, though only at trace levels. Industrial activity accounts for the potentially harmful levels of these contaminants in drinking water. Other Phase V contaminants are pesticides. These chemicals enter water supplies through run-off from fields where farmers have applied them or by leaching through the soil into ground water.

Just as their uses range widely, the health risks that led Congress to require the regulation of these contaminants range widely. Six are probable cancer-causing agents. Others can cause liver and kidney damage, or problems of the nervous system and brain.

EPA set different monitoring schedules for different contaminants, depending on the routes by which each contaminant enters the water supply. In general, surface water systems must take samples more frequently than ground water systems because their water is subject to more external influences. Systems which prove over several years that they are not susceptible to contamination can usually get state permission to reduce the frequency of monitoring.

Asbestos, for example, is unlikely to appear suddenly in a system's water. If a system has asbestos-concrete water mains and water of a certain corrosiveness, or if asbestos is present naturally in an area, the system might detect asbestos in its water. Otherwise, a system which has never detected asbestos must test for asbestos only once every nine years. If the system were ever to detect asbestos, it would have to begin more frequent monitoring.

Nitrate and pesticide levels, on the other hand, vary depending on rainfall and farmers' schedules. Systems in areas prone to nitrate problems test quarterly to track the seasonal variations. If a system does not detect contaminants in initial samples, then repeat sampling frequencies will be lower than initial frequencies.

Laboratories can measure Volatile Organic Chemical (VOC) levels with considerable accuracy in a single test that costs about $100. When monitoring shows that water being provided to consumers exceeds the legal limit, the rule requires water systems to reduce those levels. EPA believes that two types of filtration are effective in reducing high VOC levels.

An EPA study in 1993 estimated that, nationwide, water systems would spend $62 million annually to comply with the Phase I rule. While all systems would incur some water-testing costs, the 1800 systems (serving 4.5 million people) which would need new water treatment systems in order to comply with the rule would spend most of the money.

The Phase II/IIb rules cost more, a total of $118 million each year, because more water systems would require improved treatment systems. As many as 3,300 water suppliers (serving 2.9 million people) would need to improve their treatment facilities or find alternate sources of water in order to meet the standards.

The same study estimated that 340,000 people would benefit from significantly-reduced exposure to the 23 contaminants of the Phase V rule. In this case, 256 water systems would spend $45 million annually to achieve compliance with the rule.

Surface Water Treatment Rule

The Surface Water Treatment Rule (published 29 June 89/effective 31 December 90) seeks to prevent waterborne diseases caused by viruses, Legionella, and Giardia lamblia. These disease-causing microbes are present at varying concentrations in most surface waters. The rule requires that water systems filter and disinfect water from surface water sources to reduce the occurrence of unsafe levels of these microbes.

As the title suggests, this rule governs water supplies whose source of drinking water is surface water, which it defines as "all water which is open to the atmosphere and subject to surface runoff." This water, which most of the country's large water systems use, is in rivers, lakes, and reservoirs. Surface water is particularly susceptible to microbial contamination from sewage treatment plant discharges and runoff from storm water and snow melt. These sources often contain high levels of fecal microbes that originated in livestock wastes or septic systems.

Ingestion of Giardia (a protozoan) and viruses can cause problems in the human digestive system, generally in the form of diarrhea, cramps, and nausea. Legionella bacteria in water are only a health risk if the bacteria are aerosolized (e.g. in an air conditioning system or a shower) and then inhaled. Inhalation can result in a type of pneumonia known as Legionnaires' Disease.

The rule sets non-enforceable health goals, or Maximum Contaminant Level Goals (MCLGs), for Legionella, Giardia, and viruses at zero because any amount of exposure to these contaminants represents some health risk. In establishing legal limits for contaminants in drinking water, EPA can set either a legal limit (MCL) and require monitoring for the contaminant in drinking water, or, for those contaminants that are difficult to measure, EPA can establish a treatment technique requirement. Since measuring disease-causing microbes in drinking water is not considered to be feasible, EPA established a treatment technique in this rule.

All systems must filter and disinfect their water to provide a minimum of 99.9 percent combined removal and inactivation of Giardia and 99.99 percent of viruses. The adequacy of the filtration process is established by measuring turbidity (a measure of the amount of particles) in the treated water and determining if it meets EPA's performance standard. Some public water supplies that have pristine sources may be granted a waiver from the filtration requirement. These supplies must provide the same level of treatment as those that filter; however, their treatment is provided through disinfection alone. The great majority of water supplies in the United States that use a surface water source filter their water.

To assure adequate microbial protection in the distribution system, water systems are also required to provide continuous disinfection of the drinking water entering the distribution system and to maintain a detectable disinfectant level within the distribution system. The distribution system is a series of pipes that delivers treated water from the water treatment plant to the consumer's tap.

According to EPA's 1993 study, compliance with this rule costs about $534 million each year for testing and upgrading treatment systems. Most of this cost is spread among the 10,200 systems (serving 48 million people) which would need significant upgrades in equipment.

Update

Total Coliform Rule

When the news media announce a "boil water emergency," reporters often speak of a "total coliform violation." Coliforms are a group of bacteria, most of which are harmless. At first glance, it might seem strange that a harmless group of bacteria such as coliforms could cause such commotion. But like police tape and chalk outlines, coliform bacteria are often found at the scene of a crime even though they are not themselves criminals.

There are a variety of bacteria, parasites, and viruses which can cause immediate (though usually not serious) health problems when humans ingest them in drinking water. Testing water for each of these germs would be difficult and expensive. Instead, water quality and public health workers measure coliform levels. The presence of any coliforms in drinking water suggests that there may be disease-causing agents in the water.

The Total Coliform Rule (published 29 June 1989/effective 31 December 1990) set both health goals (MCLGs) and legal limits (MCLs) for total coliform levels in drinking water. The rule also details the type and frequency of testing that water systems must do.

The coliforms are a broad class of bacteria which live in the digestive tracts of humans and many animals. The presence of coliform bacteria in tap water suggests that the treatment system is not working properly or that there is a problem in the pipes. Among the health problems that contamination can cause are diarrhea, cramps, nausea and vomiting. Together these symptoms comprise a general category known as gastroenteritis. Gastroenteritis is not usually serious for a healthy person, but it can lead to more serious problems for people with weakened immune systems, such as the very young, elderly, or immuno-compromised.

In the rule, EPA set the health goal for total coliforms at zero. Since there have been waterborne disease outbreaks in which researchers have found very low levels of coliforms, any level indicates some health risk.

EPA also set a legal limit on total coliforms. Systems must not find coliforms in more than five percent of the samples they take each month to meet EPA's standards. If more than five percent of the samples contain coliforms, water system operators must report this violation to the state and the public.

When a system finds coliforms in drinking water, it may indicate that the system's treatment system is not performing properly. To avoid or eliminate microbial contamination, systems may need to take a number of actions, including repairing the disinfection/filtration equipment, flushing or upgrading the distribution system, and enacting source water protection programs to prevent contamination.

If a sample tests positive for coliforms, the system must collect a set of repeat samples within 24 hours. When a routine or repeat sample tests positive for total coliforms, it must also be analyzed for fecal coliforms and Escherichia coli (E. coli), which are coliforms directly associated with fresh feces. A positive result to this last test signifies an acute MCL violation, which necessitates rapid state and public notification because it represents a direct health risk.

The number of coliform samples a system must take depends on the number of customers that it serves. Systems which serve fewer than 1000 people may test once a month or less frequently, while systems with 50,000 customers test 60 times per month and those with 2.5 million customers test at least 420 times per month. These are minimum schedules, and many systems test more frequently.

EPA's 1993 study indicated that the annual costs associated with this rule, all of which are monitoring costs, are approximately $135 million. These costs are spread among all 173,000 public water systems in the country.

Lead and Copper Rule

The Lead and Copper Rule (published 7 June 1991/effective 7 December 1992) is substantially different from the rest of this cluster of rules. The other rules require water systems to treat water so that when it leaves their facilities, it is clean and safe to drink. This rule regulates two contaminants that nearly always taint drinking water after it leaves the treatment plant.

Lead and copper are both naturally-occurring metals. Both have been used to make household plumbing fixtures and pipes for many years, though Congress banned the installation of lead solder, pipes, and fittings in 1986. The two contaminants get into drinking water when water reacts with the metals in the pipes. This is particularly likely to happen when water sits in a pipe for more than a few hours.

The two contaminants have different health effects. Lead is particularly dangerous to fetuses and young children because it can slow their neurological and physical development. Anemia may be one sign of a child's exposure to high lead levels. Lead may also affect the kidneys, brain, nervous system, and red blood cells, and is considered a possible cause of cancer. Copper is a health concern for several reasons. At very low levels, it is necessary to the body but, in the short-term, consumption of drinking water containing copper well above the action level could cause nausea, vomiting, and diarrhea. It can also lead to serious health problems in people with Wilson's disease. Exposure to drinking water containing copper above the action level over many years could increase the risk of liver and kidney damage. To prevent these effects, EPA set health goals (MCLGs) and action levels for lead and copper.

EPA required water systems to evaluate not only the pipes in their distribution systems, but also the age and types of housing that they serve. Based upon this information, the systems must collect water samples at points throughout the distribution system which are vulnerable to lead contamination, including regularly-used bathroom or kitchen taps.

When the level of lead or copper reaches the action level in ten percent of the tap water samples, the water system must begin certain water treatment steps. An action level is different from a MCL in that while a MCL is a legal limit on a contaminant, an action level is a trigger for additional prevention or removal steps.

The rule requires water systems to apply certain treatment techniques for high lead or copper levels. At a minimum, systems must maintain optimal corrosion control. Corrosion control does not reduce the contaminant level, but helps prevent the water from being contaminated in the first place. By increasing the water's pH or hardness, water systems can make their water less corrosive, and therefore less likely to eat into pipes and absorb the lead or copper. Consumers can further reduce the potential for elevated lead levels at the tap by ensuring that all plumbing and fixtures meet local plumbing codes.

When a water system exceeds either action level, it must also assess its source water. In most cases, there will be little or none of either contaminant in the source water and no treatment will be necessary. When there are high levels in the source water, treatment of that water, in conjunction with corrosion control, further lessens the chance that consumers will have elevated levels of lead and copper at the tap.

The rule also requires systems that exceed the lead action level to educate the affected public about reducing its lead intake. Finally, a system which continues to exceed the lead action level after completing corrosion control and source water treatments may have to replace some of its lead water mains.

EPA's 1993 study estimated that the annual costs of this rule would be approximately $490 million to the 52,000 water systems (serving 156 million people) that would need to do additional monitoring or to add additional treatments.

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