OCR Document

FROM CHOLERA TO CANCER TO CRYPTOSPORIDIOSIS

JOURNAL OF ENVIRONMENTAL ENGINEERING Vol 122, No 6, JUNE 1996

By Daniel A. Okun, Honorary Member, ASCE

Kenan Professor of Environmental Engineerini. Emeritus, Univ. of North Carolina, CB 8060, Chapel Hill. NC 27599

ABSTRACT:

The introduction of piped water to cities in the mid-19th century led to the spread of cholera and typhoid in the United States and the other industrialized countries. Filtration and then chlorination around the turn of the century virtually eliminated waterborne enteric disease in the industrialized world. The development of synthetic organic chemicals following World War n and the recognition that chlorine, which is so important for disinfection, reacts with natural and other organic precursors in the water, producing carcinogenic byproducts, shifted the major emphasis in water quality in the industrial world away from infectious disease to a concern for control of trace chemical contaminants. The recent emergence of waterborne giardiasis and cryptosporidiosis is shifting emphasis back to a concern for the control of enteric infectious disease. Particularly troublesome is that water meeting current microbiological standards has been demonstrated to be responsible for dianbea1 disease. The principal conclusion to be drawn from these changes is the affirmation of the original principles for the protection of drinking water quality, that water intended for potable purposes should be drawn from the highest quality sources available, that the sources should be protected, and that the treatment must be appropriate and reliable.

THE GREAT SANITARY AWAKENING

The beginning of the modern concern for community drinking water quality began about 150 years ago in both Britain and the United States. A useful defining date would be 1842 with two remarkably different events:

New York City, in response to an epidemic of waterborne cholera that took the lives of more than 3,500 people, sought a new water supply. Faced with two options, one the closer, polluted Bronx River, and the other, the higher quality Croton River, the latter was selected despite its higher cost. The festive celebration in 1842 upon delivery of the Croton River to the city, with fountains higher than the surrounding buildings at Union Square and City Hall, marked the greatest unity of all elements in the city, possibly to this day (Blake 1956). The Croton still provides about 15% of the city's supply.

        The summer of 1842 in London was "marked by perhaps a greater incidence of unemployment, destitution, and social protest than any other in the 19th century" in words from the introduction to Edwin Chadwick's "Report on the Sanitary Condition of the Labouring Population of Great Britain." (Chadwick 1865). It marked the beginning of what Professor Gordon Fair of Harvard has called "the great sanitary awakening." The report ultimately resulted in the Public Health Act of 1848 that, for the first time, charged a government with responsibility for safeguarding the health of its population.

    Typhus, tuberculosis, and cholera, all promoted by poor environmental circumstances, and particularly cholera, which was less a respecter of financial status or class, led to the creation of the General Board of Health of England in 1848. Shortly thereafter, stimulated by Chadwick, Lemuel Shattuck (1850) prepared the "Report of the Sanitary Commission of Massachusetts," which led to the creation of the Massachusetts Statc Board of Health in 1869, the first major health agency in the U.S. Because so much of its responsibilities related to water, an engineering division was created in 1886.It is interesting to note that neither Chadwick nor Shattuck was a physician or an engineer.

WATER AND CHOLERA

At the middle of the 19th century the causes of the many common diseases of the day-cholera, typhoid, dysentery, malaria, and yellow fever-were not known. Prevalent at that time in the medical community was the miasmatic or atmospheric theory that attributed the epidemics to poisons in the air emanating from the "bowels of the earth." Dr. John Snow, physician to Queen Victoria, believed otherwise and demonstrated the verity of his hypothesis in ways that have lessons for us today. In the summer of 1849, Snow wrote, "The most terrible outbreak of cholera which ever occurred in this kingdom, is probably that which took place in Broad Street, Golden Square and adjoining streets." Within 250 yd of a popular well, "upwards of 500 fatal attacks of cholera occurred in 10 days." (Snow 1855).Fatal attacks began on August 30, 1849 reaching a peak of 143 on September I, and falling to eleven on September 9th. Snow examined the appearance of the water from the well, which was not conclusive, but took from the general registry a list of the deaths from cholera in neighborhoods radiating from the well. Some of the deaths occurred in households near other wells but, through interviews, he learned that householders had gone the extra distance to the Broad Street well because they preferred the taste of its water. A woman who succumbed from cholera during the outbreak, but who lived at a considerable distance from Broad Street, and who had not been to Broad Street for many months, was found to have arranged for a large bottle of water to be filled from the Broad Street pump and carted to her home every day. A visitor to her house from outside London who also drank from this bottle died of cholera at the same time. Snow plotted the deaths on a map that then looked like a well-used rifle target with the bull's eye at the Broad Street well.

This study was the first confirmation of Dr. Snow's hypothesis that cholera is waterborne. Snow urged the Board of Guardians of St. James parish, which owned the well and pump, to remove the handle of the pump on September 8th. By that time, the strength of the epidemic had already been spent but this action represents perhaps the first instance on record of the implementation of an appropriate measure to prevent the transmission of waterborne disease. This action was taken decades before the germ theory of disease was introduced and before cause and effect could be "scientifically" established. In 1832, during one of the first major recorded cholera epidemics in London, deaths from cholera ranged from about 10 per 10,000 to 110 per 10,000 among those using Thames River water. The introduction of piped water drawn from the Thames into the wealthier homes in London and the invention of the water closet led to the discharge of human wastes into the storm sewers that drained directly into the Thames. Cholera had become a regular visitor to London, killing the rich as well as the poor. Snow undertook a study of the transmission of cholera among the people receiving piped water from the several water companies serving London, most of which took water from the Thames. In 1849, deaths from cholera increased sharply, ranging from more than 200 pcr 10,000 for people taking from the farthest downstream intakes to fewer than 10 pcr 10,000 at the furthest upstream intakes. The increased death rate over 17 years and the death rate going down river as more sewers entered the river, justified the inference that pollution might have been responsible for the higher incidence of the disease.

The more definitive proof, and that with the most important lessons for us today, came with a later cholera epidemic that hit London. Two water companies, the Southwark and Vauxhall Co. and the Lambeth Co., were in direct competition. Most streets south of the river near the lower reaches of the river within London were being served by the two companies. These were characterized as "by far the worst of all those who take their water from the Thames, with 120 to 180 deaths per 10,000 in 1849 for each of the two companies." Snow (1855). In 1852, however, the Lambeth Company, to attract more customers, improved the aesthetic quality of its water supply by moving its intake. above sewage discharges from London. When the 1854 cholera epidemic struck, Dr. Snow saw an excellent opportunity to evaluate the different sources. Table 1 shows what he found.

<> The death rate among those drinking water from the lower Thames was 8.5 times greater than among those drinking water from the upper Thames. This was confirmation that ingestion of contaminated water was responsible for the disease.

The significance of Dr. Snow's work was to alert those responsible for community water supply to the importance of selecting the best sources available. Professor Fair, in presenting his philosophy about water supply, characterized this issue by declaring that he "preferred the virginal to the repentant, " a paraphrase of how an earlier distinguished American engineer, Allen Hazen, had put it, . 'Innocence is better than repentance." (Okun 1991).

The significance of source was recognized in the early history of modern water supply. Kober (1908) examined the typhoid rates in cities in the U.S., as shown in Table 2. New York City, with its upland supply, had the lowest rate of the 61 cities, with 15 per 100,000. Pittsburgh, with its run-of-river supply had the highest, with 120 per 100,000.

The introduction of filtration sharply reduced the incidence of enteric disease. From 1900 to 1913, as the population served with filtered water increased eightfold, the typhoid death rate in the U.S. dropped by more than 55% (Ellms 1928).

The idea that filtration might make a high quality source unnecessary began to grow. Philadelphia, which had been taking its water from run-of-river sources, was slow among the major cities to address its high typhoid rate of 75 pcr 100,000. The city administration had contended that filtration was not as effective as boiling the water. In 1900, a reform mayor was determined to address this issue. He named a distinguished panel of consulting engineers, including Rudolph Hering of New York, to recommend the best approach for enlarging the supply and making it safe, and their "report did not have any surprises." (McCarthy 1987). It recommended continued use of the Schuylkill and Delaware Rivers: "Water from upcountry sources might be preferable but the great cost of building aqueducts and upcountry reservoirs made that option very expensive and really unnecessary since filtration would provide safe water." The mayor later admitted he had favored taking water from an upcountry source but he was willing to go along with the engineers because their estimates fell within the city's borrowing capacity. Before the filters could be built, the most serious typhoid outbreak occurred, resulting in 1,063 deaths. Complete filtration was instituted finally in 1911, reducing the death rate to 13 per 100,000. New York City had reached this low rate almost 70 years earlier by developing an upland source.

In the early years of the 20th century, chlorine was introduced for public water supply disinfection which, with filtration, virtually eliminated waterborne infectious disease in the U.S. The few outbreaks that did occur were attributable to the absence or failure of chlorination (APHA 1937). Because filtration and chlorination could prevent the transmission of most of the more common causes of waterborne enteric disease, many cities elected to take water from polluted river sources because they were lower cost, even when options for higher quality water were available.

London, at the turn of the century, debated this at length. Their consulting engineers favored taking water from the mountains of Wales, available by gravity and of much higher quality than that of the Thames (Okun 1972), stating in an unpublished report that "No one acting for himself personally with regard to a water supply to his country house would allow a small difference in cost to determine whether he should go to a pure spring or to a stream into which some other house drained. . . . It appeared to us that in coming to a decision upon so vital and irrevocable a question as the additional water supply of water to London for a long series of years, the safer course would be to act for future generations as our instinctive and deep rooted feelings in favor of pure water would lead us to act for ourselves. . . it is not necessarily a wise course to accept the lowest tenders and take an inferior article where water supply is concerned." (Baker and Deacon 1897). Nevertheless, the higher cost moved the government authorities to select the Thames, downstream of major industrial cities and dependent on off-channel reservoirs for storage, as the source of water for London, which it is to this day.

<> New Orleans, now taking water near the mouth of the Mississippi River, and Cincinnati. taking water from the heavily industrialized Ohio River, might have developed groundwater sources. The latter has recently installed granular activated carbon filtration to address the problem of trace contaminants. Internationally, the many cities building water supply systems in the developing world in this century have had no hesitation in taking their water from run-of-river sources of questionable quality. The higher risk in these cities from "human frailties" has led to many instances of serious outbreaks of disease despite the presence of modern filtration and disinfection facilities. New Delhi in 1955, with more than 50,000 cases of infectious hepatitis, was an example. Municipal officials and their engineers throughout the world have generally become sanguine about the selection of their sources, given the provision of filtration and chlorination.

The history of water purification from the earliest records to the 20th century is well told in The Quest for Pure Water (Baker 1948). An indication of the low level of interest in the public health issues is indicated by the absence of the words "typhoid," "cholera," "bacteria," "health," "standards," and "regulations," among others in the 27-page index to this 527-page tome. The chapter on disinfection does mention the importance of filtration and disinfection in preventing the spread of typhoid and cholera. A brief epilogue states, "In the last 60 years (from about 1880), with advances in the arts and sciences, including the acceptance of the germ theory of disease and of water as one of the chief means of spreading cholera and typhoid, standards for the quality of water have been raised."

Drinking water standards being developed during the first half of the 20th century were directed primarily at prevention of transmission of enteric pathogens. A useful surrogate for these pathogens was the coliform test. If E.coli were absent, and current disinfection practices were followed, it had been concluded that the pathogens would also be absent. As is noted later in this paper, this can no longer be assumed to be the case.

WATER AND CANCER

The chemical revolution that accompanied and followed World War II introduced into society, the environment, and into water courses and groundwater, thousands of new synthetic organic chemicals (SOCs), most designed to be toxic to troublesome biota and designed also, for economic reasons, to be long-lasting. Society was slow to recognize the problem until Rachel Carson published Silent Spring (1962). The issue for humans was the strong possibility that long-term ingestion of even trace concentrations of these SOCs would be carcinogenic, teratogenic, or mutagenic:

"It is obvious that with the rapidly increasing urbanization and industrialization of the country and the greatly increased demand placed on the present resource of water from lakes, rivers, and underground water reservoirs, the danger of cancer hazards from the consumption of contaminated drinking water will grow considerably within the foreseeable future." (Hueper 1960).

    The U.S. Public Health Service Drinking Water Standards (1962) recognized the organic chemical issue by including for the first time a limit for carbon chloroform extractables which included all organics, synthetic and natural, toxic and nontoxic, adsorbable on granular activated carbon. In the early 1970s, the U.S. Environmental, Protection Agency (EPA) found hundreds of organic chemicals in drinking water sources, a high percentage of which were believed to be carcinogenic, teratogenic, and/or mutagenic in animals. The large number of SOCs found in the Mississippi near New Orleans, together with the results of epidemiological studies in New Orleans and vicinity that revealed somewhat higher levels of cancer among those using the filtered and chlorinated public supply drawn from the Mississippi as compared with those using untreated groundwater in the vicinity (Talbot and Harris 1974), led to the passage of the Safe Drinking Water Act (SDWA) in 1974.
<>    It was not until EPA's Interim Primary Drinking Water Regulations were published in 1976 that specific synthetic organic species were mentioned in drinking water standards; in this case six widely used pesticides (U.S. EPA 1976). Research began in earnest on additional SOCs but identifying the critical organics and establishing acceptable levels was a daunting task. The EPA contracted with the National Research Council to study the issue on its behalf, with a nine-volume set of books, Drinking Water and Health, emerging over a 13-year period (National Research Council 1977 -1989). Not incidentally, the 1976 regulations carried the following statement on water sources:

    "Production of water that poses no threat to the consumer's health depends on continuous protection. Because of human frailties associated with protection, priority should be given to selection of the purest source. Polluted sources should not be used unless other sources are economically unavailable, and then only when personnel, equipment, and operating procedures can be depended on to purify and otherwise continuously protect the drinking water supply. "EPA encourages the states to conduct sanitary surveys on a systematic basis. These on-site inspections of water systems are more effective in assuring safe water to the public than individual tests taken in the absence of sanitary surveys."

    Because the current regulations are not printed in any booklet, and additions since 1976 have been made only through publication in the Federal Register, water supply officials see few references to watershed protection in the regulations, but many references to the new maximum contaminant levels (MCLs) they are obligated to meet.

Another critical issue concerning SOCs was first recognized in 1969 by Joshua Lederburg, Nobel Prize geneticist, in a syndicated column in The Washington Post headlined "We're So Accustomed to Using Chlorine that We Tend to Overlook Its Toxicity." (Lederburg 1969). After pointing out that chlorine has saved millions of lives he wrote, "What little we do know of the chemistry of chlorine reactions is portentous. It should sometimes react. . . to form substances that may eventually reach and react with the genetic material, DNA, of body cells. .. . That chlorine is also intended to inactivate viruses should provoke questions about the production of mutagens in view of the close chemical similarity between viruses and genes. " Nevertheless, Lederburg failed in attempts to get funds from EPA to follow up on this research with his team.

    However, in 1974, Rook, in the Netherlands, demonstrated that chlorine was responsible for creating uihalomethanes (THMs), which were found to be carcinogenic in animals (Rook 1974). The problem is ubiquitous, given that disinfection byproducts (DBPs) are created when surface waters and groundwaters are chemically disinfected.

    Concern for SOCs and DBPs led the U.S. Congress to enact the 1986 Amendments to the Safe Drinking Water Act which, among many other items, obliged the EPA to establish maximum contaminant levels, and goals, for a significant number of additional contaminants. In addition, Congress obliged the EPA to add 25 new contaminants every 3 years. Fig. 1 shows the increase in the number of contaminants regulated over the last 70 years, increasing from four in 1925 to likely more than 100 by the end of the century. Most of the new contaminants are and will be SOCs, including DBPs, the latter including byproducts from other chemical disinfectants as well as chlorine.

    The situation in Europe has been much the same. Before joining the European Community (EC), drinking water standards in the United Kingdom were simply that the water be "wholesome," with its definition and regulation being the responsibility of local health authorities. The EC has followed much the same strategy as the EPA in developing its regulations, differing somewhat in details. When the UK joined the EC, its regulations were adopted. The World Health Organization has adopted guidelines for member nations which have the same framework (WHO 1993).

    The significance of SOCs in drinking water as a cause of cancer in humans is not well established nor is the risk likely to be more precisely defined in the future for many reasons.

    The MCLs are based on long-term exposure of animals to single species of SOCs, yet people are exposed to many SOCs simultaneously, some of which may be synergistic. The combinations of SOCs are very much site specific, and animal studies on mixtures of SOCs are not feasible for national standards.

    Only a very small fraction (about 15%) of the SOCs have been identified, with few of these characterized for their health effects (NRC 1977-1989).

About 50% of the halogenated organic material contributing to the total organic halide (TOX) concentrations in drinking water have not yet been identified (Singer 1994).

    The risk assessment models for the very low exposures of contaminants in drinking water have not been experimentally verified

    In the absence of identifying and determining the health significance of the myriad SOCs in water, epidemiological studies assume great importance but, unfortunately, these have not been very helpful, in part because of the extensive time periods required for cancers to emerge in exposed populations.

    Many, but not all, epidemiological studies have reported associations between chlorinated water and the mortality of colon, rectal, and bladder cancer. A moderate but significant increased risk for bladder cancer was observed among nonsmokers in a case-control study conducted by the National Cancer Institute (NCI) (Cantor et al. 1987), but a later study by the NCI was negative (Craun 1993). A widely publicized, but controversial, meta-analysis, which combined 10 previously published epidemiology studies, reported increased relative risks for bladder and rectal cancer but not colon cancer (Morris 1992).

    Despite the absence of adequate, hard, scientific proof of a significant cause-effective relationship between drinking water and cancer, much of the concern and new regulations for drinking water quality in the last quarter of the 20th century have been based on cancer risk.

DIARRHEAL DISEASES IN DEVELOPING COUNTRIES

    An important and unfortunate side effect of this concern for water and cancer, and particularly the role of chlorine and DBPs generally in possibly promoting cancer, has been the impact on developing countries. With infant mortality rates tenfold greater in developing countries than in industrialized countries, and with most of this attributable to diarrheal waterborne infectious diseases such as typhoid and cholera that have largely been eliminated in the industrialized world, disinfection of surface waters is absolutely essential. Chlorine is the disinfectant of choice in developing countries because it is by far lowest in cost. Yet the ubiquity of radio and television throughout the world, and the spread of news that the EPA is urging reduced chlorine use because chlorine is said to contribute to cancer, has induced many authorities in developing countries to reduce or even abandon the use of chlorine. The fast spread of the 1991 cholera epidemic that originated in Lima was attributed in part to fear of cancer (Salazar-Lindo 1993), with some of the blame attributed by Peruvian officials to the U.S. EPA.

    It is often claimed that, because of more limited economic and human resources in developing countries, drinking water standards need not be as restrictive as in industrialized countries. Harold Thomas provided a useful and entertaining model that first appeared in The Harvard Quarterly Journal of Economics (Thomas 1964). He hypothesized MacDonald's farm with a herd of "ferthings." Because of a contaminated well, his ferthings began to suffer from "hyfertitis" caused by a microbial pathogen in the water. The farmer had a daughter, an aspiring epidemiologist and, of course, there was a traveling salesman who had a device that could purify the water. Thomas developed a model that includes the numbers of animals, their profit (or value), the infectivity of the pathogen, their concentration in the water, the discount rate, and the cost of treatment including the discount rate and economic time horizon.

    It is customary to consider the high costs of treatment in evaluating water supply options but not the concentration and infectivity of the pathogens present in the water source. The latter may be several orders of magnitude greater in developing countries than in industrialized countries while costs of treatment may be only a little greater. Thomas's model implies that developing countries might need more rigorous standards than industrialized countries. Put another way, relaxed standards for drinking water in such situations impute a lower value to human life in developing countries.

    Trace chemical contaminant concentrations in water in Asia, Africa, and Latin America are generally less than in industrialized countries. Less attention therefore needs to be given to cancer-causing compounds in water in these countries as contrasted with the urgency of controlling infectious diseases. The EPA based its cancer risks on 70-year exposures; Hfe spans in many developing countries are on the order of 50 years. With . high mortality rates due to infectious disease, accidents, and work-related exposures, few people in these countries grow old enough to die from cancer. Clearly, the need in Asia, Africa, and Latin America is the control of infectious waterborne diseases through continued use of chlorine.

WATER AND CRYPTOSPORIDIOSIS

"Fatal Neglect" was the title of a special reprint of The Milwaukee Journal published five months after the April 1993 cryptosporidiosis outbreak in that city that caused some 400,000 people to become seriously ill, some 100 to die, and many to become permanently incapacitated (Rowen and Behm 1993). Those who did not fully recover from this diarrheal disease, (and there is not yet treatment for it) were from a large segment of the population characterized as "immunocompromised," which includes AIDS patients, those who test positive for human irnmuno-deficiency virus, cancer patients undergoing treatment, the very young, the sickly, and the elderly.

The title was chosen to reflect the newspaper's belief that, despite the EPA's knowledge about Cryptosporidium and its effects, including six earlier outbreaks of cryptosporidiosis in the United States and several in England, regulatory measures were not instituted for its control. The Surface Water Treatment Rule (SWTR) promulgated in 1989 under the SDWA did focus on giardiasis, an enteric disease similar to but milder than cryptosporidiosis, but which had appeared on the scene many years earlier, and for which there is therapy. Furthermore, giardiasis is generally self-limiting and, most importantly, Giardia cysts are readily inactivated by chlorine dosages feasibly used in water treatment. Cryptosporidium oocysts, on the other hand, are not inactivated by conventional chlorination and, being smaller in size, may more easily pass through filtration plants, requiring more careful operation of the facilities. Another major problem is that there is no surrogate for Cryptosporidium, which, if absent, signifies the absence of the pathogen. Monitoring for Cryptosporidium itself is extremely difficult. A study of 20 laboratories (Clancy et al. 1994), given water samples seeded with the cysts and oocysts of Giardia and Cryptosporidium, reported that recovery rates were generally less than 10%, although improved analyses are increasing recovery rates to about 30%. With pathogens as highly infective as these, where only a few cysts or oocysts may cause the disease, such monitoring data understate the risk.

    Human and animal wastes are the principal sources of these protozoa. Data are limited, but surveys have shown that Giardia and Cryptosporidium are ubiquitous in surface waters of the United States with concentrations found in finished drinking water ranging up to about 5/looL (Rose 1988; Rose et al. 1991; LeChevallier 1991). Some recovered cysts and oocysts may have been inactivated but, with low recovery rates, significant numbers may be present when it is appreciated that ingestion of one to 10 organisms may be sufficient for infection.

    Reported incidence rates for endemic giardiasis, which is reportable, is about 10-100 per 100,000 people. Cryptosporidiosis rates can be expected to be at least as great. Given the seriousness of exposure in a large vulnerable population, cryptosporidiosis may well be important even when no outbreaks are reported.

    One important realization has emerged from the cryptosporidiosis experience, which is that because of the dependence on indicator organisms, namely the coliforms, water that meets the EPA (and WHO) microbial standards has been assumed to be free of pathogens. This is no longer the case. There is good reason to believe that many diarrheas,. particularly those caused by parasites such as Giardia and Cryptosporidium, are waterborne even when the water meets current drinking water standards. A recent study indicated that households that received water drawn from a polluted source, but that met drinking water regulations, exhibited significantly higher rates of diarrheal episodes than similar households using the same water but equipped with point-of-use reverse osmosis membrane units (Payment et al. 1991). In the case of unfiltered supplies that meet microbial standards, waterborne endemic giardiasis and cryptosporidiosis are believed to be present but unidentified because of the absence of adequate surveillance programs. It has been estimated that even if 1,000 cases of waterborne cryptosporidiosis occurred in one week in New York City, an outbreak of cryptosporidiosis is unlikely to be detected and a waterborne source is unlikely to be recognized (Juranek 1993).

Approaches to the control of Cryptosporidium are uncertain. As noted, monitoring is difficult and turbidity and particle size measurements constitute the most significant parameters, aside from tests for oocysts, for determining their presence in surface water, although the correlation is poor. Inactivation of oocysts by chlorination is ineffective and filtration will need to be more rigorous. Measures for the control of cryptosporidiosis are likely to appear in an enhanced SWTR. Research on the control of microbial contamination which, according to The Milwaukee Journal, was neglected in favor of research on the control of potential cancer-causing sacs and DBPs, certainly deserves a higher priority today. Other parasites, bacteria, and viruses are beginning to surface, some of which may be as or more serious than Cryptosporidium.

The SWTR requires filtration of all surface waters except in the few instances where the watersheds are of almost pristine quality and where the water purveyor can "demonstrate through ownership and/or written agreements with landowners within the watershed that it can control all human activities which may have an adverse effect on the microbiological quality of the source water." However, EPA has no regulations for watershed protection if filtration is provided, and thereby permits a heavy burden to be placed on the treatment facilities.

CONCLUSION

The re-emergence of waterborne infectious disease as a significant health risk in industrialized countries is stimulating a new emphasis on the importance of source water quality and the protection of watersheds. What can be said without contradiction is that, in the face of microbial contaminants such as Cryptosporidium, which are not readily monitored, inactivated, or removed, and in recognition that monitoring and protection against the older diarrheal diseases is stilI not yet very effective in many developing countries, much more attention needs to be given to selection of the best sources available and protection of those sources through land use controls and sanitation measures on the watersheds. Also, more rigorous water treatment practices, particularly involving filtration processes are necessary to reduce the risk of exposure to parasites in the environment.

Our concerns have become similar to those which troubled our forebears 150 years ago, stimulating the need for protection against infectious waterborne enteric disease. We should be better equipped to handle them.

REFERENCES

American Public Health Association. (1937). "Waterborne outbreaks in the U.S. and Canada. 1930-1936. and their significance." Annu. Year Book. 120(2).

Baker. M. N. (1948). 1M quest for pure water. American Water Works Association, Denver, Colo.

Baker. Sir B.. and Deacon, G. F. (1897). "Report to the London County Council." Rep.. Institution of Civil Engineers. London. England.

Blake. N. M. (1956). Water for the cities. Syracuse University Press.

Cantor. K. P., et al. (1987). "Bladder cancer. drinking water source and tap water consumption: A case-control study." J. Nat. Cancer Inst.. 19(6), 1269-1279.

Carson. R. (1962) Silent spring. Houghton, Mifftin. New York, N.Y.

Chadwick, E. (1842). Rep. on the sanitary condition of the labouring population of Great Britain. Edinburgh Univ. Press, Edinburgh, United Kingdom, 1965.

Clancy, J. L., Gollnitz, W. D., and Tabib, Z. (1994). "Commercial labs: How accurate are they?" J. AWWA, 86(5), 89-97.

Ellms, J. W. (1928). Water purification. McGraw-Hill, New York, N.Y. Hueper, W. C. (1960). "Cancer hazards from natural and artificial water pollutants." Proc.. Con/. on Physiological Aspects of Water Quality, U.S. Public Health Service, Washington, D.C.

Juranek, D. (1993). "Cryptosporidium and cryptosporidiosis. Centers fordisease control and prevention." AWWA Water Quality Con/., AWWA,Denver, Colo.

Kober. G. M. (1908). "Conservation of life and health by improved water supply." Engrg. Rec., 57(June).

LeChevallier, M. W., Norton, W. D., and Lee, R. G. (1991). "Giardia and Cryptosporidium in filtered drinking water supplies." Appl. Envlr. Microbiol., 57(9), 2610-2616.

Lederburg, J. (1969). "We're so accustomed to using chlorine that we tend to overlook its toxicity." The Washington Post. (May 3), p. A15.

McCarthy, M. P. (1987). 'Typhoid and the politics of public health in nineteenth-century Philadelphia. Am. Philosophical Soc., Philadelphia, Pa.

Moms, R. D., Audet, A. M., Angelillo, I. F., Chalmers, T. C., and Mosteller, F. (1992). "Chlorination, chlorination byproducts and cancer: A meta-analysis." Am. J. Public Health, 82(955).

National Research Council. (1977-1989). Drinking water and health. National Academy Press, Washington, D.C., Vol. 1-9.

Okun. D. A. (1972). "Health aspects of water management, public works and society." Proc., Joint Conf. of Amer. Soc. Civ. Engrs. and Inst. of Civ. Engrs., (UK), 1331-66.

Okun, D. A. (1991). "Clean water and how to get it" J. New England Water Works Assoc., 105(1), 1-10.

Okun, D. A. (1993). Global water supply issues from a public health perspective In safety of water disinfection: Balancing chemical and microbial risk. ILSI Press, Washington, D.C., 31-38.

Payment, P., Richardson. L.. Siemiatycld, J.. Dewar, R., Edwardes, M.. and Franco. E. (1991). "A randomized trial to evaluate the risk of gastrointestinal disease due to consumption of drinking water meeting current microbiological standards." Am. J. of Public Health, 81(6), 703-708.

Rook, J. J. (1974). "Formation of haloforms during chlorination of natural waters." Water 7'natment and Examination, 23(2). 234-243.

Rose, J. B. (1988). "Occurrence and significance of Cryptosporidium in water." J. AWWA, 80(2). 53-58.

Rose, J. B., Gerbs, C. P., and Jacobowsld, W. (1991). "Survey of potable water supplies for Cryptosporidium and Giardia. .Envir. Sci. and Technol., 25(8), 1393-1400.

Rowen, J., and Behm, D. (1993). "Fatal neglect." The MilwauJue Journal. (Sept. 19-26).

Safety of water disinfection: Balancing chemical and microbial risks. (1993). G. F. Craun, ed., lLSl Press, Washington, D.C.

Salazar-Lindo, E. (1993). "The Peruvian cholera epidemic and the role of chlorination in its control and prevention." Safety of Water Disinfection: Balancing Chemical and Microbial Risk, lLSI Press, Washington, D.C.

Shattuck, L. (1850). Rep. of the Sanitary Commission of Massachusetts. Harvard Univ. Press, Cambridge, Mass.

Singer, P. C. (1994). "Issues and concerns for the control of disinfection by-products." J. Envir. Engrg. Div., ASCE, 120(4),727-744

Snow, J. (1936). "Snow on cholera." Oxford Univ. Press, London, England.

Talbot, P., and Harris. R. H. (1974). The implications of cancer-causing substances in Mississippi River water. Envir. Defense Fund, Washington, D.C.

Thomas, H. A. Jr. (1964). "The animal farm." J. AWWA, 56(9), 1089-1091.

U.S. Environmental Protection Agency. (1976). "National interim primary drinking water regulations." 40 FR 59565, 40 CFR 141, U.S. EPA, Washington, D.C.

U.S. Public Health Service. (1962). "Drinking water standards." PHS Publication No. 956, Washington. D.C.

World Health Organization. (1993). Guidelines for drinking water quality. Vol. 1. recommendations. 2nd Ed.. Geneva.

TABLE 1. Data of John Snow on Cholera In London, 1854

Water service and source	Number of houses served	Deaths from cholera	Deaths per 100,000 households

Sothwark and Vaushall Co from Thames River at London	40,046	1,263	315
Lambeth Co.: from Thames River above London	26,106	98	37
Rt of London: we& andsurface sources	256,423	1,422	59

TABLE 2.

Mean Typhoid Death Rates in US 1902-1906

Number of

Death rate

cities per 100,000

(2) (3)

4 18.1

18 18.5 8 19.3 7 33.1 5 45.7 19 61.6

Source (1)

Ground water

Impoundments and protected watersheds Small lakes

Great lakes

Mixed surface and groundwater Run-of-river supplies