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“When you fill a glass with water from your tap, you expect to drink water that is pure and safe. But how safe is it?
Water contains impurities from natural and man-made sources, such as minerals, gases, bacteria, metals and chemicals. Many of these impurities are harmless. However, some impurities can adversely affect your health. Others can damage equipment, stain laundry and fixtures and emit odors.
To protect the public health and ensure uniform standards for water quality nationwide, Congress passed the Safe Drinking Water Act of 1974. This act and its amendments authorized the U.S. Environmental Protection Agency (EPA) to establish limits on the concentration of certain contaminants in public water supplies (systems serving more than 25 people or 15 year-round connections). Private water supplies, including wells, are not regulated by drinking water standards. The owner must test and treat the water as needed to avoid health risks.”
Extension Housing & Environment Specialist
Department of Housing and Consumer Economics
The EPA standards for drinking water fall into two categories – Primary Standards and Secondary
EPA regulations develop Primary Standards for drinking water based on three criteria:
In setting Primary Standards for a drinking water contaminant, research scientists first look at all the toxicological data on that water contaminant. This data is usually the result of studies that have been conducted on animals. Occasionally human clinical or epidemiological data are also available. Scientists use this information to estimate the concentration of a drinking water contaminant that may be toxic and the concentrations, if any, that may cause no adverse effects.
The levels of contaminants found in drinking water are seldom high enough to cause acute health effects – effects that occur almost immediately after exposure to a large dose of a substance. Therefore, scientists are most concerned about chronic health effects such as cancer, birth defects, miscarriages, nervous system disorders and organ damage. These health effects may occur after prolonged exposure to small amounts of a substance. When scientists set drinking water standards, they treat contaminants that cause cancer (carcinogens) differently from contaminants that cause other health effects.
In setting Primary Standards for substances believed to cause cancer, research scientists assume that no concentration is safe. Consequently, the MCLG is set at zero. But a zero level is not always possible to achieve, so regulators estimate toxicity by calculating a figure called a risk estimate.
In theory, any concentration of a carcinogen in your drinking water may possibly cause cancer. In practice, however, at very low concentrations the risk of cancer becomes so small that it is considered negligible. Therefore, scientists must decide what level of risk is acceptable. It may be one excess cancer in 10,000 persons or one excess cancer in 1 million persons exposed over a lifetime (70 years). The concentration of the substance estimated to cause this acceptable level of risks is the risk estimate. Based on the risk estimate, EPA regulators establish the MCLs for cancer-causing contaminants.
Setting drinking water standards is an imperfect process. Data relating human health effects to contaminants in drinking water are limited, and scientists have difficulty predicting the effects of drinking small amounts of a substance for many years. In addition, regulatory decisions frequently incorporate economic, political and social considerations.
Although current drinking water standards do not guarantee that the glass of water you draw from your tap will be absolutely safe and pure, they do reflect sound scientific judgment. Standards are based on all available knowledge.
For non-carcinogenic toxic substances, scientists set standards using a figure calculated from animal studies called the reference dose. The reference dose is the amount of a substance that a person can consume daily, over a lifetime, without suffering any adverse health effects. It includes a conservative margin. The reference dose used to be called acceptable daily intake.
EPA regulators use the reference dose to establish a Maximum Contaminant Level Goal (MCLG) for a water contaminant. The MCLG is the concentration of a contaminant that experts believe a person can consume safely over a lifetime. It is based entirely on health considerations and is set at a level where no adverse health effects should occur. The MCLG is not enforced by the EPA. It is the goal used to set enforceable drinking water standards.
Under the Safe Drinking Water Act, the primary role of the federal government is to develop national drinking water regulations that will protect public health and welfare. The states have the responsibility for monitoring public water systems and enforcing drinking water standards for EPA – regulated contaminants and other contaminants. The local public water systems are responsible for treating and testing drinking water to ensure that water quality consistently meets the standards set by the regulation.
When levels go above a standard, the EPA requires that the water contaminant levels be reduced to the Maximum Contaminant Level. The corrective treatment is left to the public water system. In addition, Federal law requires that the water system must notify the public when a drinking water standard has been violated. Public notification must include clear explanations of the violations; information on potential adverse health effects; the steps being taken to correct the problem; and the need, if any, to seek alternative water supplies. This procedure is a safety precaution intended to keep the public informed and call attention
Under the Safe Drinking Water Act Amendment of 1986, consumers have the right to obtain the following information about their drinking water:
Protection under the Safe drinking water Act of 1974 includes:
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