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How Safe Is My Drinking Water?

Introduction

Most community water suppliers deliver high quality drinking water to millions of Americans every day. Of the more than 55,000 Community Water Systems in the United States, only 4,769 or 8.6 percent reported a violation of one or more drinking water health standards in 1996.

Nationwide, drinking water systems have spent hundreds of billions of dollars to build drinking water treatment and distribution systems, and they spend an additional $22 billion per year to operate and maintain them. Additional monies became available in 1997 to upgrade drinking water systems and implement local source water protection activities.

In addition, there is a network of government agencies whose job is to ensure that public water supplies are safe. Nonetheless, problems with local drinking water can, and do, occur.

Why Does EPA Allow Any Contaminants in Drinking Water?

All sources of drinking water contain some naturally occurring contaminants. Because water is the universal solvent, many materials are easily dissolved upon contact. At low levels, these contaminants generally are not harmful in our drinking water. Removing all contaminants would be extremely expensive and in nearly all cases would not provide greater protection of health. A few of the naturally occurring substances may actually improve the taste of drinking water and may have nutritional values at low levels.

What Problems Can Occur?

As development in our modern society increases, there are growing numbers of threats that could contaminate drinking water. Suburban sprawl has encroached upon once-pristine watersheds, bringing with it all of the by-products of our modern life style. Actual events of serious drinking water contamination occur infrequently, and typically not at levels posing near-term health concern. Nonetheless, with the threats of such events increasing, we cannot take drinking water safety for granted. Greater vigilance by you, your water supplier, and your government is vital to ensure that such events do not occur in your water supply.

Microbiological and chemical contaminants can enter water supplies. These materials can be the result of human activity or can be found in nature. For instance, chemicals can migrate from disposal sites and contaminate sources of drinking water. Animal wastes and pesticides may be carried to lakes and streams by rainfall runoff or snow melt. Human wastes may be discharged to receiving waters that ultimately flow to water bodies used for drinking water. Coliform bacteria from human and animal wastes may be found in drinking water if the water is not properly treated or disinfected. These bacteria are used as indicators that other harmful organisms may be in the water.

The potential for health problems from drinking water is illustrated by localized outbreaks of water-borne disease. Many of these outbreaks have been linked to contamination by bacteria or viruses, probably from human or animal waste. In 1993 and 1994, for example, there were 30 reported disease outbreaks associated with drinking water, 23 associated with public drinking water supplies and 7 with private wells.

Certain pathogens, such as Cryptosporidium, may pass through water treatment filtration and disinfection processes in sufficient numbers to cause health problems. Cryptosporidium is a protozoa that causes the gastrointestinal disease cryptosporidiosis. The most serious, and sometimes deadly, consequences of cryptosporidiosis tend to be focused among sensitive members of the population, such as individuals with immune system deficiencies.

A 1993 outbreak of cryptosporidiosis in Milwaukee, Wisconsin, is the largest outbreak of waterborne disease in the United States. Lake Michigan is the source of Milwaukees water, which is treated by filtration and disinfection. Due to an unusual combination of circumstances during a period of heavy rainfall and runoff the treatment plant was ineffective, resulting in an increase in the turbidity of the treated water. Increased turbidity can be, and was in this case, an indicator of higher levels of Cryptosporidium. Over 400,000 persons were affected by the disease, more than 4,000 were hospitalized, and over 50 deaths (some counts are as high as 100) have been attributed to the disease. The original source of contamination is uncertain.

Nitrate in drinking water at levels above the national standard poses an immediate threat to young children. Excessive levels can result in a condition known as "blue baby syndrome." If untreated, the condition could be fatal.

Boiling water contaminated with nitrate increases the nitrate concentration and the potential risk. Persons worried about nitrate should talk with their doctor about alternatives to using boiled water in baby formula.

Naturally occurring contaminants also are being found in drinking water. For example, the radioactive gas radon-222 occurs in certain types of rock and can get into ground water. People can be exposed to radon in water by drinking it, while showering, or when washing dishes. The primary source of exposure to radon in the home is radon seeping out of the soil and into the basement air.

Where Can I Get More Information About My Water?

Information on water quality in your area is available from several sources, including your local public health department and your water supplier. You can determine whom to contact by checking your water bill or by calling your local town hall.

State agencies also can provide extensive information on your water supply and its quality. Each state has a department responsible for drinking water quality.

EPA maintains general water resources information at its headquarters and in its 10 regional offices. Other groups, such as environmental organizations, also may be able to provide information.

How Does EPA Set Drinking Water Standards?

EPA has issued drinking water standards, or Maximum Contaminant Levels (MCLs) for more than 80 contaminants. The standards limit the amount of each substance allowed to be present in drinking water.

A process called risk assessment is used to set drinking water quality standards. When assessing the cancer and non-cancer risks from exposure to a chemical in drinking water, the first step is to measure how much of the chemical could be in the water. Next, scientists estimate how much of the chemical the average person is likely to drink. This amount is called the exposure. In developing drinking water standards, EPA assumes that the average adult drinks 2 liters of water each day throughout a 70-year life span.

Risks are estimated separately for cancer and non-cancer effects. For cancer effects, a risk assessment estimates a measure of the chances that someone may get cancer because they have been exposed to a drinking water contaminant. EPA generally sets MCLs at levels that will limit an individuals risk of cancer from that contaminant to between 1 in 10,000 and 1 in 1,000,000 over a lifetime. For non-cancer effects, the risk assessment estimates an exposure level below which no adverse effects are expected to occur.

MCLs are set based on known or anticipated adverse human health effects, the ability of various technologies to remove the contaminant, their effectiveness, and cost of treatment. All MCLs are set at levels that protect public health. The limit for many substances is based on lifetime exposure so, for most potential contaminants, short-term exceed-ances pose a limited health risk. The exceptions are the standards for coliform bacteria and nitrate, for which exceedances can pose an immediate threat to health.

To comply with MCLs, public water systems may use any state-approved treatment. When it is not economically or technologically feasible to set an MCL for a contaminant--for example, when the contaminant cannot be easily measured--EPA may require use of a particular treatment technique instead. The technique specifies the design for part of the drinking water treatment process.

How Many Public Water Systems Have Exceeded The MCLs And Treatment Requirements?
Currently, the nations approximately 55,000 Community Water Systems (CWSs) must test for more than 80 contaminants. In 1996, 4,151 systems, or 7 percent, reported one or more MCL violations, and 681 systems (less than 2 percent) reported violations of treatment technique standards.
Who Makes Sure That My Drinking Water Supply Is Safe?

Local governments, public water systems, the states, and EPA work together towards the goal of ensuring that all public water supplies are safe. For households on private wells, state and local health departments usually have some standards for the drinking water, but it is generally up to the homeowner to maintain the quality of the drinking water.

Local governments have a direct interest in protecting the quality of their drinking water source, be it ground water or surface water. They may be responsible for overseeing land uses that can affect the quality of untreated source water. Public water systems have a responsibility to maintain sound treatment works and water distribution networks. They are responsible for ensuring that the water they supply does not contain contaminants at levels higher than the law allows.

Prior to 1974 each state ran its own drinking water program and set the standards that had to be met at the local level. As a result, drinking water protection standards differed from state to state. Since 1974, when Congress passed the original Safe Drinking Water Act, EPA has set uniform nationwide minimum standards for drinking water. State public health and environmental agencies have the primary responsibility for ensuring that these federal drinking water quality standards, or more stringent ones required by the state, are met by each public water supplier.

When a state water agency or water supplier announces that the standard for a particular contaminant has been exceeded, that may or may not by itself be a cause for alarm, but it can be a cause for action. It is a safety precaution required by the law to alert the public to deficiencies in drinking water quality.

Boil Water Notices

When microorganisms such as those that indicate fecal contamination are found in drinking water, water suppliers may be required to issue "boil water notices." Boiling water kills the organisms that can cause disease. Therefore, the notices serve as a precaution for the public.

Boil water notices are being issued more frequently in recent years. In fact, in 1993 notices were issued by water suppliers in New York City and the District of Columbia, which together serve more than 7.1 million people. At least 725 other communities have also issued notices affecting almost 3 million people in the past few years.

U.S. Environmental Protection Agency
1200 Pennsylvania Avenue, NW
Washington, DC 20460
www.epa.gov