.

April I O , 1996 The Friday Center

Chapel Hill, North Carolina Sponsored by North Carolina A W A / WEF

Brief Resume Daniel A. Okun

Daniel A. Okun is Kenan Professor of Environmental Engineering, Emeritus at the University of North Carolina at Chapel Hill, where he has been since 1952 in the Department of Environmental Sciences and Engineering. He has long been a proponent of dual distribution systems, one for potable water and the other for reclaimed water for nonpotable urban uses. His keynote address at the Annual American Water Works Association Conference in Cleveland, Ohio in 1968 proposed consideration of dual systems. He was involved in the planning of the first, and st i l l today the largest, municipal dual system in the world in St. Petersburg, FX in 1973. In the 1970s, he was employed by the California State Department of Health Services to review the water reclamation and reuse program in California which at that time had a well-developed set of regulations and the most extensive program of nonpotable reuse in the United States, including the innovative Irvine Ranch Water District dual distribution system. Since then he has been involved in water reclamation and nonpotable urban water reuse projects and programs throughout the United States and in Asia, Africa and Latin America. L

He has participated in the preparation of the first and second editions of Guidelines for Water Reuse, published by the U.S. Environmental Protection Agency in 1980 and 1992, respectively, and in the preparation of the American Water Works Assodation manual of water supply practice Dual Water Systems, published originally in 1983, with a second edition in 1994.

Prior to coming to the University of North Carolina, where he served as head of the Department of Environmental Sciences and Engineering from 1955 to 1973, Dr. Okun had served with the U.S. Public Health Service on the Ohio River Pollution Survey, in the U.S. Army in the Pacific during World War II, and as a consulting engineer with Malcolm Pirnie in New York. Since his retirement from UNC, he has been working as a consultant in water-related projects throughout the world.

Dr. Okun received B.S. and M.S. degrees in Civil Engineering from Cooper Union and Cal Tech and his doctorate in sanitary engineering from Harvard.

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A History of Nonpotable Water Reuse Through Dual Distribution Systems‘

Daniel A. Okun Kenan Professor of Environmental Engineering, Emeritus

University of North Carolina Chapel Hill, NC 27599-8060

bv

Nonpotable urban reuse, largely through dual distribution systems, is of recent vintage. Because of rapid urban growth throughout the world, local water shortages have become increasingly frequent, even in humid regions. Accordingly, the production of reclaimed water to replace drinking water that is used for nonpotable purposes in urban areas has begun to receive considerable attention.

The practice of wastewater reclamation and reuse had its modem birth in the mid-19th Century with the introduction of sewerage systems for conducting household wastes away from communities into the nearest water courses, a practice which exploded with the rapid adoption of water closets.

*The considerable pollution of the Thames as it passed through London not only caused nauseating conditions in the city but was responsible for repeated epidemics of cholera among those being served with public water supply taken from the Thames. The solution was the construction of a vast interceptor which, in following the admonition of Sir Edwin Chadwidc “The rain to the river and the sewage to the soil,” carried the wastewater for spreading on “sewage farms.’’ Such ‘land treatment“ became widely adopted by the larger cities in Europe.

The growth of urban sewerage led to increased discharges of wastewaters untreated or with various degrees of treatment to water courses which downstream often served as sources of water supply for other communities. This so-called “indirect potable reuse,’ led to high mortality rates from cholera, typhoid and other diarrheal diseases. At about the tum of the century, the development of filtration and then chlorination sharply reduced enteric disease in the industrialized countries. However, in the cities of Asia, Africa and Latin America, waterborne disease rates continue to be high and the threats of cholera epidemics are ever-present. In addition, the use of these waters for irrigation of market crops continues to be a major hazard to the residents of these cities, and to visitors as well, as generally no treatment is afforded to the wastewaters or to the waters abstracted from the rivers for irrigation. These problems have been well documented (Okun 1991).

The subject of this paper is the reclamation of wastewater and its reuse for nonpotable purposes in cities through dual systems. This has evolved as

‘ For presentation at a Seminar on Water Reclamation and Reuse sponsored by the N.C Section of the AWWA and the N.C. Water Environment Association in Chapel Hill, N.C on April 10, 1996.

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2 an important option in water resources planning in urban areas for two important reasons: (1) it provides an additional source of water and (2) it reduces the cost of wastewater disposal.

An Additional Source of Water

Figures 1 and 2 illustrate the rapid rate of population growth in the world and the increasing proportion of that population growth which is in urban settings. This has resulted in inadequate sources of high quality waters for many urban areas, initially in arid and semi-arid regions but, in the last several decades, in very humid regions as well.

Many cities had followed public health principles in developing their water supplies, namely:

'Traduction 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 be used only when other sources are economically unavailable and then only when the provision of personnel, equipment and operating procedures can be depended upon to purify and otherwise protect the drinking water supply continuously.” (U. S. Public Health Service 1962)

This principle was incorporated in the primary drinking water regulations promulgated by the U. S. Environmental Protection Agency when it took over responsibility for community water supply with the passage of the Safe Drinking Water Act of 1974 (USEPA 1976). Unfortunately, many cities had begun ignoring this principle when it appeared that filtration and chlorination could render waters drawn from polluted sources safe from infectious disease. Concern for the quality of the source did revive following World War II, when it began to be appreciated that polluted sources could contain anthropogenic chemicals that pose health risks when ingested over long periods of time even at trace concentrations. Also, it was found that waters rich in organic matter, when disinfected with chlorine, produced disinfection by-products which were a health threat when ingested over long periods. More recently, outbreaks of giardiasis and cryptosporidiosis have given evidence that conventional water treatment might not be entirely adequate for the prevention of these infectious diseases and others which have not yet been well-identified. Cities drawing from such compromised sources of water are needing to invest in higher degrees of treatment at considerably greater cost. To invest in such treatment and the extensive monitoring associated with it to assure its continued safety is very costly, particular when most of the water used within a city does not need to be of potable water quality. Moreover, such treatment is not always reliable.

Cities that elected to follow public health principles and develop protected upland sources found that their sources served them well but with

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3 urban growth they were no longer adequate in yield. Adding to their high quality sources has become very difficult for several reasons: such additional sources are more distant and much more costly to develop or water rights to additional sources might not be available. In any case, the cost of developing additional high quality sources is becoming very great. In recognition of this, the United Nations Social and Economic Council, in 1958, enunciated a policy that “No higher quality water, unless there is a surplus of it, should be used for a purpose that can tolerate a lower grade.” (UN 1958) When it is recognized that only a very small fraction of the water used in urban areas is required to be of potable water quality, this policy makes sense. Reclaimed water used for the myriad nonpotable purposes in a city conserves the limited high quality waters for potable purposes for a much larger population. While the policy has been slow to be adopted, it is now beginning to see a rapid rate of growth through the construction of dual distribution systems: one system, from a high quality source, for potable purposes and the other, reclaimed water also of high quality but not suitable for drinking, for nonpotable purposes in households, commerce, industry, and public facilities, including especially amenities such as landscape irrigation, public fountains, lakes and environmental improvements.

A Lower Cost Amroach to Pollution Control.

While the need for additional public water supply has emerged as the major reason for investing in water reclamation and reuse in urban areas, its initial impetus in the United States came from reducing the cost of wastewater treatment and disposal. With the increasing rigorous requirements for disposal of wastewaters to streams, lakes, and the ocean, particularly for the removal of nutrients, reclamation and nonpotable reuse has often emerged as less costly than treatment for discharge. These initial dual systems were affordable even though they were retrofitted which is, of course, considerably more costly than installing distribution system lines during construction of city streets.

In application, both lowerast sources of additional water and lower- cost disposal of wastewaters have entered into the adoption of dual systems. The current status of the practice of urban nonpotable reuse is fully covered in-EPA’s second edition of its Guidelines for Water Reuse, a 247-page publication which includes all types of reclamation and reuse and lists state standards and regulations where they exist, as well as having a chapter on international practices (US EPA 1992).

Nonpotable - Urban Uses

Nonpotable and industrial uses of reclaimed water justify special attention, particularly as compared with uses for agricultural irrigation, in that the value of water in urban use is considerably greater than its value in agricultural irrigation. The urban and industrial applications promise full cost recovery which is appropriate for urban and industrial water supply

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4

systems whereas the value in agricultural irrigation other than for highly specialized market crops, is not likely to recover costs.

Urban uses include:

Irrigation of parks, athletic fields, school yards, highway medians and shoulders, and areas around public buildings and facilities; irrigation of landscaped areas around single-family and multi-family dwellings; and irrigation of private landscaped areas around commercial and industrial buildings, golf courses, nurseries and the like. Irrigation is an attractive urban use because reclaimed water is rich in nutrients generally eliminating the need to add fertilizers.

Commercial uses such as vehicle-washing, window-washing, water for the application of biocides and liquid fertilizers, and concrete production in rapid-mix and on-site uses.

Ornamental uses such as in fountains, reflecting pools, and augmenting the flow in urban streams that go dry as a result of development.

Toilet and urinal-flushing in commercial, industrial and residential buildings, with greatest application in multi-story facilities.

Fireprotection, which is important not so much because of the volume of potable water that would be conserved, because this would very small, but because it would allow the potable water lines to be sized for delivery only of the potable water and not for the much greater fire flows. This would help avoid a major problem that arises in almost all urban distribution systems where water pipelines designed to provide fire flows carry little water except during fires, resulting in degradation of water quality because of the long residence time of water in the pipelines which results in disappearance of chlorine residuals and permits the growth of troublesome biofilms.

Industrial Uses. When a single industry or group of industries in an industrial area can use a substantial amount of reclaimed water, a dedicated line may be provided, with the reclaimed water of a quality suited to the needs of the customers. More commonly, industries are scattered throughout a community and the reclaimed water is distributed to all residential, commercial and industrial customers. Those industries that have special water needs, such as required for special papers, instruments, and the like, requiring especially high-quality water, would be obliged to provide this themselves much as is done even where highquality potable water is available. Industrial uses include make-up water for evaporative cooling towers, boiler-feed water, process water, and irrigation of plant grounds. Evaporative cooling water is the most widely used application in industry. Industrial process applications that have found reclaimed water entirely suitable for their purposes include pulp and paper manufacture, chemical

.

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manufacture, textiles, petroleum and coal products, steel manufacture and industrial production where the product would pose no health risk to consumers.

In the United States, particularly in the arid and semi-arid areas in the southwest and in humid Florida, landscape irrigation has been by far the major urban use. Industrial uses within a city have had to be negotiated on a case-by-case basis and are slowly increasing in number. Vehiclewashing and the use of reclaimed water for construction have grown to be popular. Toilet and urinal-flushing with reclaimed water is just beginning in the U.S. but is widely practiced in Japan (Maeda et al1995).

Where landscape irrigation is the major use, it tends to be highly seasonal, requiring storage facilities of considerable size to conserve reclaimed water produced during wet periods to meet the high requirements during dry periods. Development of the other urban uses would redue seasonal variations.

- Reclaimed Water Oualitv for Urban Nomotable Reuse

Requirements for reclaimed water to be used for nonpotable pu~poses was first addressed in California where the so-called “Title 22” Regulations were adopted in 1972 and last revised in 1978 (California 1978). Their successful application without untoward incidents led to their adoption by other states. To date, there are no federal regulations for nonpotable reuse. EPA’s Guidelines, however, specify degrees of treatment and quality standards for a wide range of uses with the most stringent being for unrestricted urban use where large populations are likely to be exposed and for irrigation of so- called “market crops.“ In brief, the treatment includes the filtration of secondary effluents followed by disinfection to produce water with average turbidity equal to or less than 2 NTU, and a maximum not to exceed 5 NTU, with no detectable fecal coliform in 100 ml, and a minimum chlorine residual of 1 mg/L after a minimum contact time of thirty minutes. With regard to microbiological quality, this is the equivalent of drinking water standards, so that inadvertent ingestion even for a period of time would not pose a health risk. There are no requirements with regard to organic chemicals but, because the water is not to be ingested for long periods of time, trace contaminants including disinfection by-products are not an issue.

Historv of Dual Svstem

The first dual distribution system in the United States was built to provide water supply for a rapidly growing Grand Canyon Village in Arizona

. on the south rim of the canyon where rainfall is sparse and no sources of water exist. Water for the village was originally brought in by tankers over roads and rails into the village until a spring, about 1 km (0.6 miles) deep in the canyon, was developed from which water was pumped to the village. The wastewater produced was too valuable to be discarded and so it began to

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6 be treated and reclaimed for landscape irrigation and toilet-flushing in 1926 (Garth & Gilbert 1968). As the village grew, the system was renovated and enlarged, the last time in 1989, even after an additional source of water was developed on the north side of the canyon and piped down to the river and up to the village (Fleming 1990). In addition to the original uses for landscape irrigation and toilet-flushing in the visitor area, its uses have extended to serving the permanent village for staff employees, including schools and service buildings, as well as for vehiclewashing, cooling water make-up, construction and other nonpotable uses.

Many reclamation and nonpotable use projects in urban settings were thereafter developed for single or groups of large users not necessarily involving comprehensive dual reticulation systems. One of the most noteworthy was the construction in 1942 of a 2.4-m (96-inch) pipeline 7.2 km (4.5 miles) from the Baltimore Back River activated sludge plant to deliver about 4.5 m3/s (100 mgd) to the Sparrows Point plant of the Bethlehem Steel Company for process use, cooling water being provided by once-through passage of water obtained from a nearby water course. This reclamation program served to sigruficantly reduce the demand on Baltimore's limited 'upland supply and simultaneously reduced wastewater discharge from the city to local receiving waters (Okun 1973). In the years following, many power plants began to used reclaimed water for cooling tower make-up. A related power plant use was that for the TECO Power Plant, near Tampa, Florida which uses seawater for oncethrough cooling but purchases almost the entire production of a small tertiary reclamation plant for stack gas scrubbing to reduce air pollution.

In some regions, committing all or most of the available reclaimed water from a large city to a single large user may be a mistake. In 1982, a 58- km (%-mile) transmission main was placed in operation to carry secondary effluent from Phoenix, Arizona to a 3.9 m3/s (90-mgd) reclamation plant at the Palo Verde Nuclear Power Plant for cooling. The several owners of the power plant and the city of Phoenix were sued by a Phoenix land developer over the a rights to the reclaimed water which he believed was needed for residential and commercial development in and around the city. While the suit was lost, the need for conservation of the reclaimed water resulted in the power plant increasing the efficiency of its cooling towers, reducing its need for makeup to only about half the original demand, releasing reclaimed water for other uses within the city.

A large scale municipal dual system for the sale of reclaimed water to urban customers was established on a limited basis in Colorado Springs in 1960 (Okun 1973). Because of the demand for high quality sources of water for

. the rapidly growing region at the foot of the Rocky Mountains, about one third of the secondary effluent from Colorado Springs was given tertiary treatment, rapid sand filtration and disinfection with chlorine, for sale to large-scale irrigation customers such as college campuses, golf courses, cemeteries and other large urban users. The desirability of this water was

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7 evinced by the fact that it was in great demand at a price of about two-thirds of that of the available potable water.

Dual water supplies had been suggested by the late Professor Gordon M. Fair of Harvard at meetings of the Subcommittee on Water Supply of the Committee on Sanitary Engineering and Environment of the National Research Council in the 1950s and developed by Paul Haney who wote the first paper on dual systems in 1965 (Haney & Hamann 1965).

Planning of the first major comprehensive urban dual system in the United States to serve all customers was initiated in St. Petersburg, Florida in 1969 by the late Lloyd Dove, then Director of Public Works, after extensive discussions with the author who had made a keynote presentation at the 1968 American Water Works Association Annual Conference in Cleveland promoting the idea that wastewater reclamation for nonpotable urban use in a dual distribution systems would present an option that should be considered by cities facing requirements for additional urban water supply. Interest in the paper was stimulated by the initial refusal of the Journal editor to publish the paper. He agreed to publish only if rebuttals would be permitted, a condition which the author heartily endorsed, believing that more journal papers should be accompanied by discussions. Rebuttals were duly prepared by Samuel Baxter, then Commissioner of the Philadelphia Water Department, and Henry Graeser, then Director of Water Utilities for Dallas, Texas, with Albert Halff, a Dallas consultant. The author followed-up with a closing statement (Okun 1969a). Other papers in the same vein were published by the author at about the same time (Okun 1968 a,b,c, 1969 b; Okun & McJunkin 1971).

The initiative for the St. Petersburg system came principally from the economies that might be realized as a result of new florida regulations requiring nutrient removal prior to discharge of effluents to Tampa Bay and the Gulf of Mexico. The lower cost of tertiary treatment, filtration and chlorination, and federal grant funds under the Construction Grant Program at that time made reclamation and reuse more economical. Because the initial objective was wastewater disposal and agricultural irrigation, users were not metered. A flat rate per acre to be irrigated was designed to encourage maximum use of the reclaimed water.

The St. Petersburg system was retrofitted with filtration and disinfection added at the four treatment plants serving different quadrants of the city. The reclaimed water reticulation system was sized to include provision for fire protection, although the potable water system already included fire protection. Covered service reservoirs for the reclaimed water at the treatment plants were introduced after difficulties were experienced

. using open water storage facilities due to the proliferation of algae, a not surprising outcome with nutrient-enriched waters exposed to the considerable sunlight. During periods of low demand and during extensive rainy periods, the excess effluent produced was injected into deep wells

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8

penetrating saline aquifers that underlay the city. The original intention was the creation of a freshwater bubble in the aquifer from which the reclaimed water might later be withdrawn for use during high demand periods. The design of the disposal wells proved to be unsuitable and the reclaimed water spread out widely and was not readily recoverable. Studies are now underway to reexamine design of the wells with the intention of permitting recovery of the reclaimed water because St. Petersburg is now experiencing a considerable shortage of reclaimed water in dry periods. With more than 8000 residential customers, landscape irrigation dominated the demand. There has been excessive wastage of the reclaimed water and plans are now underway to retrofit meters on all customer services. Many other uses have also developed: air-conditioning, toilet-flushing, cooling towers for its resource recovery power plant, vehicle-washing, garden nurseries, watering of soft tennis courts and major league baseball training fields.

As the situation in St. Petersburg evolved, the major benefit to the city became the savings in the demand on its high quality water source. Water for St. Petersburg and other water utilities in the vicinity comes from a limited groundwater aquifer with well fields some 50 km (30 miles) north of the city in Pasco County. Excessive withdrawals from these well fields by the communities served by the Southwest Florida Water Management District has contributed to the drying up of lakes in the so-called ''Land of Lakes" region. St. Petersburg is the only city in the region whose demand on the well field has decreased despite its growth in population since the reclaimed water system has been placed in operation, as shown in Figure 3 (Johnson 1992).

At about the same time that St Petersburg inaugurated its system, the relatively new city of Irvine, California, which had begun with a conventional water system, initiated installation of reclaimed water lines for all new construction. This was driven in part by the need for control of wastewater disposal to the sea but the major factor was the high cost of water purchased by the Irvine Ranch Water District (IRWD) from the Metropolitan Water District of Southem California (MWD) and the expectation, very soon realized, that the cost of MWD water would increase significantly.

While Imine had the benefit of installing reclaimed water lines during new construction, it has found it currently economical to return to the older parts of the city and retrofit reclaimed water pipelines. Incidentally, even during the heyday of the several construction grants programs have provided much of the funds for many community wastewater treatment plants, the IRWD did not use them. All of their investment in dual systems was undertaken because it was more economical. For example, Imine has been the first city to use its reclaimed water for toilet-flushing on a large scale, a requirement for all its new high-rise office buildings (Young et al 1994). Irvine's reclamation plant is typical of many in soLithem California in that it is located near the water markets and is not obligated to handle the solids which are conveyed to a terminal plant. This makes it acceptable to site reclamation plants in residential and commercial areas.

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The IRWD meets its seasonal storage requirements by the use of surface storage which, because reclaimed water is rich in nutrients, stimulates algae growth and requires refiltration and disinfection for all water drawn from these reservoirs. Diurnal variations in demand, on the other hand, are met by covered service reservoirs.

The Future

Dual distribution systems are finding continually wider use in the United States, with many states being obliged to develop regulations for urban reuse. Two such are Washington and North Carolina, both enjoying high levels of precipitation. Dual systems have become economically attractive to individual cities in humid regions because the ability of many of these cities to develop new sources of water has been sharply curtailed both because of their high marginal cost and because of the political and environmental difficulties involved in building impoundments and abstracting waters that originate on the property of other local governments.

An interesting development of a dual distribution system is that for a new community, Rouse Hill, to accommodate about 250,000 people near Sydney, Australia, . All households are being fitted with potable and reclaimed water services inside individual units for toilet flushing. Water for fie-protection is provided only from the reclaimed water system. As mentioned earlier, this was not done as a water conservation measure, as relatively little water is used for fire-fighting, but rather to reduce the size of the potable water pipelines to preserve drinking water quality.

It is not difficult to envisage a future, when potable water lines can deliver water drawn from high quality sources and/or from plants with high quality treatment, and high quality pipe materials will be used for the potable service, all because the amount of water needed to be of drinking water quality will be relatively small and costs will therefor be affordable. In fact, membrane treatment, which is hard to justify for conventional systems where much of the water is used for such nonpotable purposes as landscape irrigation and toilet-flushing, would be affordable if directed only at the water supplies that are intended for drinking.

Considerable interest is being shown in water reclamation and reuse for potable purposes. Many cities have embarked upon such projects without evaluating the nonpotable option in a realistic manner. The vision of a reticulation system with pipe lengths twice that of a mnventional system seems to lead to the rejection of the nonpotable option on its face, as being too costly. That such systems are being built without subsidy is evidence that they are not inherently more costly. Even if they were somewhat higher in cost, customers have shown a much greater preference for using reclaimed water for nonpotable purposes than for drinking (USEPA 1992). Experience has also demonstrated that where the microbiological quality of reclaimed

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10 water is a little different from that required for potable water, there is an accepted assurance of its safety even were it to be inadvertently ingested for short periods of time. Acceptance of dual systems by the profession is indicated by AWWA's publication of Manual 24 on dual systems in 1983, with a second edition published in 1994 (AWWA 1994).

For those who are concerned with the quality of drinking water, history has demonstrated that concerns for potable water quality have grown tremendously over the years since drinking water standards were first adopted in the United States. Figure 4 illustrates the increase in the number of contaminants for which maximum contaminant limits have been imposed over the years. According to the National Academy of Sciences, only about 15% of the organics in water have been identified, let alone characterized as to their health significance and only about 50% of disinfection by-products have been so characterized. It can be expected that as time goes on, drinking water requirements will become more rigorous and the preference for a high quality source will emerge more strongly than when the EPA Drinking Water Regulations were promulgated in 1976.

Nonpotable reuse permits more appropriate uses of limited high quality sources while imposing less public health risk than where potable reuse is projected. Historical trends would seem to support continued growth of the nonpotable reuse aption in the future with limited adoption of planned potable reuse.

References

American Water Works Assn. 1994. Dud Water Systems (h4.24). Second Edition.

California State Department of Health Services. 1978. Wastewater Reclamation Criteria. California Administrative Code, Title 22, Div. 4.

Fleming, P.A. 1990. Water Supply, Reclamation and Rew at Grand Canyon: A Case Study. Proceedings of Conserv 90, Phoenix, AZ.

Garthe, E.C. and Gilbert, W.C. 1968. Wastewater Reuse at the Grand Canyon. J. WPCF. 40:1582.

Haney, P. and Hamann, C.L. 1965. Dual Water Systems. 1. AWWA, 571073.

Johnson, W. 1992. Director of Public Works, City of Petersburg, as published in Guidelines for Water Reuse.

Maeda, M., Naicada, IC, Kawamoto, K. and Ikeda, M. 1995. Area-wide Use of Reclaimed Water in Tokyo, Japan. Proceedings, Section Int'l. Symposium on Wastewater Reclamation and Reuse, Int'l. Assn. on Water Quality, Book 1, pp. 55-62, Iraklio, Greece.

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11

Okun, D.A. 1968. The Hierarchy of Water Quality. Environmental Science and Technology, 2 672.

Okun, D.A. 1968c, The Future of Water Quality Management. 1967 Croll Memorial Lecture. Published in J. Institute of Water Pollution Control (Britain). 1:7.

Okun, D.A. 1969. Alternatives in Water Supply, Keynote Address, 1968 AWWA Annual Conference. 61: 215.

Okun, D.A. 1969. New Developments in Urban Water Supply. J . Japan Water Works Assn. 414: 54, March.

Okun, D.A. 1973. Planning for Water Reuse. J. AWWA, Denver, CO, 65:617.

Okun, D.A. 1991. A Water and Sanitation for Strategy for the Developing World. Environment, Heldref Publishers. Washington, D.C. 33(8): 16.

'Okun, D.A. A Water Quality Hierarchy for Arid Lands. Arid Lands in Perspective. Univ. of Arizona Press, Tucson, pp. 2914 (1968)

Okun, D.A. and McJunkin, F.E. 1971. Feasibility of Dual Water Supply Systems, Seventh Annual h e r . Water Resources Conf., Chicago. p. 129.

U.S. Environmental Protection Agency. 1976. National Interim Primary Drinking Water Regulations 40 FR 59565; 40 CFX 141.

U. S. Environmental Protection Agency. 1992 Guidelines for Water Reuse, EPA/625/R-92/004.

U.S. Public Health Service. 1962 Drinking Water Standards, Washington, DC, PHS Publication No. 956.

United Nations Economic and Social Council. 1958. Water for lndustrial

.Young, RE., Holliman, T.R, and Parsons, J. 1994. Using Reclaimed Water for Bathroom Flushing - A Case History, Proceedings 1994 Water Reuse Symposium. AWWA/WEF. pp. 721-34.

Use. UN Report No. E/3058ST/ECA/50. UN, New York.

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12 Figure 3

Estimated Potable Water Conservation Achieved Through Urban Reuse City of St. Petersburg, Florida

Figure 4 Number of Contamlnants In Drlnklng Water

Regulated by U.S. Government

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City of SL Petersburg, Florida !mated Potable Water Conservatlon Ac5leved Through Urban Reuse

Figure 4 Number of Contamlnants In Drlnklng Water

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