The Drinking Water Standards

When the objective of water treatment is to provide drinking water, then we need to select technologies that are not only the best available, but those that will meet local and national quality standards. The primary goals of a water treatment plant for over a century have remained practically the same: namely to produce water that is biologically and chemically safe, is appealing to the consumer, and is noncorrosive and nonscaling. Today, plant design has become very complex from discovery of seemingly innumerable chemical substances, the multiplying of regulations, and trying to satisfy more discriminating palates. In addition to the basics, designers must now keep in mind all manner of legal mandates, as well as public concerns and en-vironmental considerations, to provide an initial prospective of water works engineering planning, design, and operation.

The growth of community water supply systems in the United States started in the early 1800s. By 1860, over 400, and by the turn of the century over 3000 major water systems had been built to serve major cities and towns. Many older plants were equipped with slow sand filters. In the mid 1890s, the Louisville Water Company introduced the technologies of coagulation with rapid sand filtration.

The first application of chlorine in potable water was introduced in the 1830s for taste and odor control, at that time diseases were thought to be spread by odors. It was not until the 1890s and the advent of the germ theory of disease that the importance of disinfection in potable water was understood. Chlorination was first introduced on a practical scale in 1908 and then became a common practice.

Federal authority to establish standards for drinking water systems originated with the enactment by Congress in 1883 of the Interstate Quarantine Act, which authorized the Director of the United States Public Health Services (USPHS) to establish and enforce regulations to prevent the introduction, transmission, or spread of communicable diseases.

Today resource limitations have caused the United States Environmental Protection Agency (USEPA) to reassess schedules for new rules. A 1987 USEPA survey indicated there were approximately 202,000 public water systems in the United States. About 29 percent of these were community water systems, which serve approximately 90 percent of the population. Of the 58,908 community systems that serve about 226 million people, 51,552 were classified as "small" or "very small. " Each of these systems at an average serves a population of fewer than 3300 people. The total population served by these systems is approximately 25 million people. These figures provide us with a magnitude of scale in meeting drinking water demands in the United States. Compliance with drinking water standards is not

uniform. Small systems are the most frequent violators of federal regulations. Microbiological violations account for the vast majority of cases, with failure to monitor and report. Among others, violations exceeding SDWA maximum contaminant levels (MCLs) are quite common. Bringing small water systems into compliance requires applicable technologies, operator ability, financial resources, and institutional arrangements. The 1986 SDWA amendments authorized USEPA to set the best available technology (BAT) that can be incorporated in the design for the purposes of complying with the National Primary Drinking Water Regulations (NPDWR). Current BAT to maintain standards are as follows:

For turbidity, color and microbiological control in surface water treatment: filtration. Common variations of filtration are conventional, direct, slow sand, diatomaceous earth, and membranes.

Turbidity

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