National Drinking Water Clearinghouse
West Virginia University
P.O. Box 6064
Morgantown, WV
26506-6064

Safe Water Should Always Be on Tap

by Kathy Jesperson
On Tap Managing Editor
kjespers@wvu.edu

 

Editor’s Note: This is the final installment of a three-part series on the history of drinking water treatment and waterborne disease. See the summer and fall 1996 issues of On Tap for previous articles.

“Americans have a right to know what’s in their drinking water and where it comes from,” said President Clinton during the ceremony at which he signed the reauthorized Safe Drinking Water Act (SDWA) into law, according to an August 7, 1996, Washington Post article. “Americans have a right to trust that every precaution is being taken to protect their families from dangerous, and sometimes even deadly, contaminants.”

But the path to modern drinking water tech-nology is a long one that we have yet to finish. Centuries of experimentation, research, and trial and error among scientists and engineers have progressed in a determined direction. But much more needs to be done.

The 19th century brought several pioneering researchers. The work of individuals, such as Robert Koch and Louis Pasteur—who established the germ theory of infectious disease—and John Snow—the man who recognized the relationship between a single water source and illness—made it possible to develop sanitation methods and water treatment practices that provide people with safe drinking water.

Along with the understanding that microorganisms were responsible for most waterborne diseases came drinking water rules and regulations. Standards have been set for drinking water contaminants, includ-ing lead, copper, nitrates, total coliform, and trihalomethanes. Once set, water systems have a responsibility to maintain the standards.

Maintaining drinking water standards requires sophisticated treatment methods, which may include coagulation, flocculation, sedimentation, filtration, disinfection, and aeration.

Coagulation, Flocculation, Sedimentation

Flocculation and coagulation require that chemical substances be added to water prior to sedimentation.

“Suspended particles in water can affect drinking water’s color and taste, interfere with filtration and chemical disinfection, increase the concentration of disinfection by-products produced during chlorination or other disinfection, and provide ideal bases for the growth of potentially harmful bacteria and other microorganisms,” Safe Water Should Always Be on Tap writes Eric Olson in Victorian Water Treatment Enters the 21st Century, a Natural Resources Defense Council March 1994 publication.

“Although the chemicals used in these tech-niques are relatively new, the techniques themselves are not,” he notes.

Coagulants, such as almonds, toasted biscuits, powdered ginger, cornmeal, crushed oyster shells, and alum, were found in civilizations as diverse as the Chinese, Arabian, and Indian as early as 2,000 B.C., according to the August 1996, American Water Works Association publication, Opflow.

In the last quarter of the 19th century, coagu-lants were first used in municipal water plants. In most cases, coagulation was not a separate process. It was used in conjunction with filtration, and was widely used to precede rapid sand filtra-tion after 1885. Coagulation, used as a treatment for public water supplies, initially caused much debate. Even though this method had been widely used for household purposes for centuries, those unfamiliar with its water-clarifying qualities shunned its use. Putting something foreign into drinking water to purify it was beyond the imagi-nations of some scientists and researchers, explains M.N. Baker in the Quest for Pure Water.

“I imagine there were similar arguments when Louis Pasteur refined the pasteurization process,” says David Pask, National Drinking Water Clearinghouse technical services coordinator.

Today, coagulation is an integral part of water treatment in many modern treatment facilities. Modern coagulants include aluminum sulfate (or alum), lime, iron, iron salts, and organic coagulant polymers. Coagulants react with other substances in the water, causing them to clump together. This reaction makes removal of impurities—usually accomplished through filtration—much easier.

Coagulation is usually followed by floccula-tion, a process that gently agitates the water to mix suspended particles, causing them to collide and form heavier particles called floc. Then, through sedimentation, these heavier particles settle out of the water before it is filtered.

“Sedimentation is the simplest method of water treatment,” notes Olson, adding that “merely allowing water to stand for 24 hours, using no other techniques, removes 90 to 95 percent of suspended matter” from the water.

The process has been used for centuries, he states. Olson uses a description by Frontinus, a 51 B.C. historian, to make his point: “The river . . . flows muddy and discolored . . . for this reason a settling reservoir was built upstream from the intake, so that in it and between the river and the conduit the water might come to rest and clarify itself.”

In 1829, the first sedimentation tank in America was installed in Lynchburg, Virginia. The modern version of the settling tank dates to the 1920s, with updated versions appearing in the 1950s and 1960s, Olson writes. After treatment using coagulants and flocculants accompanied with sedimentation, filtration is the next step in drinking water treatment.

Filtration in America

“Filtration in America made a bold and early—but unsuccessful—start in 1832 with an upward-flow backwash filter at Richmond, Virginia,” writes Baker. By the end of the 19th century, however, filtration was an important part of water treatment.

This method strains water through sand beds or other types of filter media, such as crushed anthracite coal, to eliminate material that is not removed through sedimentation, writes Olson. It is also an effective way of removing many disease-causing microorganisms from water, he continues.

Baker notes that America made three major contributions to filtration:

1) the introduction of rapid sand filtration,
2) vast improvements in slow sand filtration, and
3) the use of chlorination in conjunction with filtration.

Rapid sand filtration was most definitely an American product, writes Baker. Designed, tested, and implemented in the U.S., rapid sand filters became the mainstay of water filtration in the country. Many versions of the rapid sand filter sprang up, including the Hyatt, Warren, National, American, and Jewel filters. Each had its own patent, but operated under the same principle, notes Baker.

Patents were granted for designs with false perforated bottoms or a reverse-flow wash to clean the filter. Mechanical sand agitators, which also help to clean the filter, were first patented in the U.S. in 1858. Later, Patrick Clark received a patent in 1880 for a design that used vertical jets of water to clean filter media supported on a false bottom.

Some of the earliest publicity for rapid sand filters was found in an advertisement in Croes’ Statistical Tables of American Water Works in 1887. The ad claims that since the installation of the National filter at several separate locations, no infection from cholera or typhoid had been found, writes Baker.

Despite such claims, rapid sand filtration still had a long way to go. The Louisville, Kentucky, experiments, which were conducted from 1895– 1897, aided in perfecting the method, writes Baker. At the Louisville Water Company, the turbid waters of the Ohio River could not be treated using slow sand filtration—much to the dismay of Chief Engineer Charles A. Hermany.

He had noted that part of the prob-lem occurred because the reservoir was too small to obtain clear water through settling, writes Baker. Mean-while, the water company’s president was investigating a plan for a series of experimental filtration tests, using the designs of four different companies, writes Baker.

According to George W. Fuller, Louisville’s chemist and bacteriologist, all four filters failed. Even though the combination of sedimentation, coagulation, and filtration proved to be the correct principle, as used at Louisville, rapid sand filters had several weaknesses—which included inadequate storage space.

However, the greatest lesson learned from these experiments was that there is no substitute for pretreatment, notes Baker. And in spite of the weaknesses, the tests pushed rapid sand filtration in the right direction, leading to the multi-step treatment methods of today.

Disinfection

According to Baker, “Disinfection, or germ killing, first more or less incidentally and with vague or no ideas as to the how and why, then with intent and under scientific control, has been practiced for millenniums.” Disinfection agents include heat, chlorine, and ozone.

In early civilizations, people boiled their water to improve its taste and clarity. Hippocrates declared that boiling and straining rainwater was necessary to prevent it from having a bad smell and causing hoarseness. Aristotle advised Alexander the Great not to allow his soldiers to drink from stagnant pools, but to carry boiled water into the desert.

Today, chlorination is by far the most widely used disinfectant. “Nothing in the field of water purification came into use as rapidly and widely, once it got started, as chlorination,” writes Baker.

The element chlorine was discovered in the 1800s through a process that separates salt water into chlorine, hydrogen, and sodium hydroxide, notes the Chlorine Chemistry Council (CCC). The council notes that chlorine’s disinfectant qualities were first used in 1846 in the maternity ward of the Vienna General Hospital in Austria to prevent “child bed fever.”

In 1905, chlorine was added to London’s water supply, and a raging typhoid epidemic suddenly ceased. Then in 1908 its use at the Boonton Res-ervoir of the Jersey City Water Works vaulted chlorine into action as a large-scale disinfectant in the U.S.

According to Olson, the widespread use of chlorine to disinfect drinking water supplies began during World War I to reduce the risk of waterborne disease. “The use of chlorine clearly resulted in major public health gains by virtually eliminating waterborne typhoid and cholera outbreaks in the U.S.”

Today 90 percent of U.S. public water supplies are disinfected with chlorine, notes the CCC. Besides killing disease-causing organisms, chlorine also:
• removes unpleasant tastes and odors from algae and decaying natural vegetation;
• effectively controls microorganisms,such as slime bacteria and molds, that tend to grow on the walls of transmission mains and treatment basins;
• eliminates or reduces organic coloration; and
• destroys hydrogen sulfide and removes ammonia and other compounds that have unpleasant tastes and impede disinfection.

Although the use of chlorine has been a boon to the public’s health, it does have its drawbacks— such as disinfection by-products, notes Olson. He writes: “There is ample evidence that trihalo-methanes and other dangerous by-products are formed by the reaction of free chlorine with dissolved organic materials (from human and animal sources such as urban and farm runoff, or from natural material such as decaying leaves) in drinking water."

These disinfection by-products have been linked to increasing cancer risks and birth defects, he continues. The risk from by-products can be reduced by applying drinking water treatment, such as coagulation/flocculation and sedimentation.

However, because of these risks, other methods of disinfection are being investigated. Ozonation was first used in Oudshoon in the Netherlands in 1893 and has shown promise in eliminating Cryptosporidium and Giardia, cites Olson. It also has been found to have beneficial effects on the taste and odor of drinking water, he states, adding that ozone’s oxidizing abilities aid in removing many organic contaminants. In addition, it does not seem to produce the disinfection by-products that chlorination does.

Olson also notes that ozone is the most com-monly used disinfectant in Europe. Approximately 1,000 major European water systems rely on ozone. Despite its advantages, it remains relatively unused in the U.S.

But it is not without its risks, Olson states. In water sources high in bromine—which is often found on the West Coast and in some of Florida’s waters—ozone reacts with bromine to form bromate, a suspected carcinogen. Other ozonation by-products include aldehydes and carboxylic acids—but little is known about their toxicity, Olson writes. But these compounds can be removed if water is filtered soon after disinfection.

Another factor to consider is ozone’s short residual time, which creates potentially dangerous situations in the distribution system. If there is insufficient time with a disinfectant, harmful microbes may survive. Because of this risk, many water treatment experts add a secondary disinfectant, such as chlorine, to finished water that protects it during distribution.

Aeration

Olson notes that we have evidence that aeration has been practiced for at least two centuries. He cites a poem by Edward Baynard, M.D., which expresses the benefits of aerating drinking water:

“Give it Motion, Room, and Air Its purity will ne’er impair.”

The aeration method was originally developed to ensure adequate levels of dissolved oxygen in water supplies. However, modern drinking water professionals have found it is also effective for removing volatile organic contaminants (VOCs), including certain industrial chemicals, pesticides, and radon, writes Olson.

The first aeration system in the U.S. was installed at the Elmira, New York, Water Works in 1860, Olson states, adding that since the basic techniques were developed hundreds of years ago, little has changed. The techniques involve either cascading water down a series of steps— generally known as packed tower aeration— or spraying water into the atmosphere. Olson remarks that adding aeration to a drinking water system could virtually eliminate contamination from VOCs.

Quest Continues

“Drinking water treatment has progressed from a crude craft to a scientifically based discipline,” writes Edward H. Winant, Ph.D., National Small Flows Clearinghouse technical assistant, in a paper titled A Century of Water Treatment, 1804–1902. He notes that through the years, drinking water treatment methods improved from sand filters to an integrated, multi-step process.

“What is most interesting,” Winant asserts, “is that most advances in water treatment occurred as empirical attempts at progress, with scientific justification coming later. Indeed, some engineer-ing advances were based on prevailing medical opinions that were flat-out wrong, and still yielded viable treatment procedures.

“Even more miraculous is the fact that most of the empirical attempts were evaluated on the basis of their ability to clarify water and not on potential harmful side-effects. In spite of this, the treatment methods chosen were benign and even healthful. It would certainly seem that God has smiled on the engineers involved in the quest for pure water."

References

American Water Works Association. 1996. Opflow 22:8.

Baker, M.N. 1981. The Quest for Pure Water. Volume I. Denver: AWWA.

Chlorine Chemistry Council. 1996. Chlorine and Drinking Water: Here’s to Your Health. Arlington, Virginia.

Chlorinators Incorporated. 1996. A Look Back in Time. Palm City, Florida.

Community Resource Group. 1996. Community Water Bulletin. 119:1–4.

Olson, Eric. 1994. Victorian Water Treatment Enters the 21st Century. Natural Resources Defense Council. Washington, DC.

U.S. Environmental Protection Agency. 1991. Manual of Small Public Water Supply Systems. Office of Water. Washington, DC.

Winant, Edward H. 1995. A Century of Water Treatment, 1804–1902. West Virginia University, Morgantown, WV.