3
Technologies for the Small System

Most source waters used for public drinking water supplies are not of suitable quality for consumption without some form of treatment. The U.S. Environmental Protection Agency (EPA) has ruled that all surface waters must be filtered and disinfected before consumption unless the purveyor can justify avoidance of filtration; some surface waters also need to be treated with additional processes to remove chemical contaminants before they are suitable for use as drinking water. Many ground water sources are disinfected, and many are treated to remove nuisance chemicals (such as iron and manganese) and chemical contaminants before distribution. This chapter evaluates water treatment processes that can be used by small systems and discusses their suitability under various conditions.

The fundamental responsibility of a public water system is to provide safe drinking water, as defined by the Safe Drinking Water Act (SDWA) and its amendments. Water utilities are required by the SDWA to monitor drinking water quality. When source water used by a water system does not meet quality requirements, the utility has several options. The first that should be considered is finding a cleaner, safer source water that requires less treatment than the existing source water, for this is often the most cost- and resource-efficient way to meet demand. Surface water sources tends to be turbid and typically contain higher concentrations of colloidal and microbiological material than ground water sources. Ground water sources generally have higher initial quality and tend to require less treatment than surface water sources, making ground water sources a good choice for small water systems. In fact, as shown in Table 3-1, most small systems already use ground water sources. Before installing new treatment systems, a small utility using surface water might seek a ground water source, or a



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--> 3 Technologies for the Small System Most source waters used for public drinking water supplies are not of suitable quality for consumption without some form of treatment. The U.S. Environmental Protection Agency (EPA) has ruled that all surface waters must be filtered and disinfected before consumption unless the purveyor can justify avoidance of filtration; some surface waters also need to be treated with additional processes to remove chemical contaminants before they are suitable for use as drinking water. Many ground water sources are disinfected, and many are treated to remove nuisance chemicals (such as iron and manganese) and chemical contaminants before distribution. This chapter evaluates water treatment processes that can be used by small systems and discusses their suitability under various conditions. The fundamental responsibility of a public water system is to provide safe drinking water, as defined by the Safe Drinking Water Act (SDWA) and its amendments. Water utilities are required by the SDWA to monitor drinking water quality. When source water used by a water system does not meet quality requirements, the utility has several options. The first that should be considered is finding a cleaner, safer source water that requires less treatment than the existing source water, for this is often the most cost- and resource-efficient way to meet demand. Surface water sources tends to be turbid and typically contain higher concentrations of colloidal and microbiological material than ground water sources. Ground water sources generally have higher initial quality and tend to require less treatment than surface water sources, making ground water sources a good choice for small water systems. In fact, as shown in Table 3-1, most small systems already use ground water sources. Before installing new treatment systems, a small utility using surface water might seek a ground water source, or a

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--> TABLE 3-1 Water Source for Community Water Systems of Various Sizes   Water Source   Population Served Ground Water Surface Water Small systems Under 500 91% 9% 501-3,300 74% 26% 3,301-10,000 58% 42% Large systems 10,001-100,000 46% 54% More than 100,000 28% 72%   SOURCE: EPA, 1994. utility using a poor ground water source might develop a new well in an alternative location or use a deeper aquifer by extending the depth of a well or drilling a deeper one. In either case, if alternative sources of high-quality raw water are not available, the utility might seek a source of treated water from a water utility that has an adequate supply of water and is located close enough to extend a transmission main at an affordable cost. If such options cannot be found, however, then the utility needs to explore adding additional treatment systems. Treatment Technologies: Overview Table 3-2 lists treatment processes according to the water quality problems they address. No single process can solve every water quality problem. Rather, a utility must choose from a wide range of processes that are used for different purposes. The treatment technology or combination of technologies to be used in a specific situation depends on the source water quality, the nature of the contaminant to be removed, the desired qualities of the treated water, and the size of the water system. For very small systems, treatment may not be a feasible alternative because of the high cost of having a treatment system designed and installed and the complexity of maintaining it. Historically, the design of drinking water treatment systems has been driven by the need to remove microbial contaminants and turbidity. Microbial contaminants are the central concern because they can lead to immediate health problems. Turbidity is a concern not only because water containing particles can have an objectionable taste and appearance but also because particles of fecal matter can harbor microorganisms, and soil particles can carry sorbed contaminants such as pesticides and herbicides. Aesthetic problems such as excess hardness, which

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--> TABLE 3-2 Treatment Technologies by Contaminant Type   Disinfectants/Oxidants   Air Stripping Systems   Free Cl2 NH2Cl CIO2 O3 Ultraviolet Radiation KMnO4 Aeration Membrane Aeration General water quality parameters   Turbidity   Color   X   X     Disinfection byproduct precursors   Taste and odor   X X X X X Biological contaminants   Algae   Protozoa   X X   Bacteria X X X X X   Viruses X X X X X   Organic chemicals   Volatile organic compounds (VOCs)   X X Semivolatile compounds   X Pesticides   Biodegradable organic matter  

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--> Inorganic chemicals   Hardness (calcium and magnesium)   Iron X     X   X X X Manganese X     X   X X X Arsenic   Selenium   Thallium   Fluoride   X X Radon   Radium   Uranium   Cations   Anions   Total dissolved solids   Nitrate   Ammonia  

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-->   Adsorption Systems   Powdered Activated Carbon Granular Activated Carbon Ion Exchange Activated Alumina General water quality parameters   Turbidity   Color X X     Disinfection byproduct precursors X X     Taste and odor X X     Biological contaminants         Algae   X     Protozoa   X     Bacteria   X     Viruses   X     Organic chemicals   VOCs X X     Semivolatile compounds X X     Pesticides X X     Biodegradable organic matter X X    

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--> Inorganic chemicals   Hardness     X   Iron   Manganese       X Arsenic       X Selenium       X Thallium     X   Fluoride   Radon     X   Radium   Uranium     X   Cations     X   Anions   X     Total dissolved solids     X   Nitrate     X   Ammonia  

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-->   Membrane Processes>   Microfiltration Ultrafiltration Nanofiltration Reverse Osmosis Electrodialysis/ Electrodialysis Reversal General water quality parameters   Turbidity X X X     Color   X X X   Disinfection byproduct precursors   X X X   Taste and odor   Biological contaminants   Algae X X X     Protozoa X X X X   Bacteria   X X X   Viruses     X X   Organic chemicals   VOCs   Semivolatile compounds   X   Pesticides     X X   Biodegradable organic matter  

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--> Inorganic chemicals Hardness     X X X Iron   X Manganese   X Arsenic       X X Selenium       X X Thallium       X X Fluoride       X X Radon   Radium       X X Uranium       X X Cations       X X Anions       X X Total dissolved solids       X X Nitrate       X X Ammonia  

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-->   Filtration Systems   Direct Filtration Conventional Filtration Dissolved Air Flotation Diatomaceous Earth Filtration Slow Sand Filtration Bag/Cartridge Filters Lime Softening General water quality parameters   Turbidity X X X X X   X Color X X X   Disinfection byproduct precursors X X X   X     Taste and odor   X     Biological contaminants   Algae   X X X       Protozoa X X X X X X X Bacteria X X X X X   X Viruses X X X X X   X Organic Chemicals   VOCs   Semivolatile compounds   Pesticides   Biodegradable organic matter   Xa Xa   Xa Xa  

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--> Inorganic chemicals   Hardness   X Iron X X X X     X Manganese X X X X     X Arsenic   X   X Selenium   X Thallium   Fluoride   Radon   Radium   X Uranium   Cations   X Anions   Total dissolved solids   Nitrate   Ammonia Xa Xa   Xa Xa     a Operated in biologically active mode.

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--> can lead to scaling of water heaters and excess soap consumption, and objectionable tastes and odors have also played an important historical role in the development of drinking water treatment technologies. Finally, the corrosivity of the water has been a long-standing concern because of the need to protect water mains and plumbing. Drinking water treatment systems are still designed primarily with these objectives in mind rather than being based on the need to remove trace levels of synthetic chemicals to comply with requirements of the SDWA and its amendments. Because so many regulations apply to drinking water, small systems must look at the entire spectrum of drinking water regulations before deciding on a treatment method. The system manager who considers the regulations and other water concerns on a piecemeal basis can end up using first one process and then another until finally the treatment plant becomes a costly chain of processes inefficiently tacked on to one another. Eventually the small system could find that it can no longer afford to install further treatment systems, and the whole investment might be made for naught. A number of the treatment processes listed in Table 3-2 and described in more detail below are available to small communities as package plants. The term ''package plant" is not intended to convey the concept of a complete water treatment plant in a package. Rather, a package plant is a grouping of treatment processes, such as chemical feed, rapid mixing, flocculation, sedimentation, and filtration, in a compact, preassembled unit. To provide a complete treatment plant, other equipment, or in some cases a series of package plants, generally is required. For example, most package plants designed to provide water filtration are not also equipped with equipment for disinfection, corrosion control, or adsorption of organic contaminants by granular activated carbon (GAC). Some manufactures prefer to call package plant "preengineered" process equipment because the process engineering for the package plant design has been done by the manufacturer. What remains for the water system's engineer to design is the specifics of the on-site application of the equipment. Because package plants do not require custom design, and because the process facilities (for example, mixing chamber, flocculation basin, sedimentation basin, and filter) are built in a factory instead of on-site, such systems have the potential to provide significant cost savings to small communities. Table 3-3 outlines important capital considerations for common water treatment processes. Water treatment technologies change constantly. As shown in the table, at any given time they fall into one of several broad categories: Conventional technologies are in widespread use and familiar to practicing treatment engineers and operators. Accepted technologies are not as widely used as conventional technologies. Sometimes these technologies have been developed for other fields and adopted by the water community. Some process of this type have performed

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--> Monitoring programs generally include raw and treated water sample collection, meter reading, field analyses (measuring pH, dissolved oxygen concentration, and other parameters) as appropriate, shipment of samples to a laboratory, and recordkeeping. The use of state-approved sampling methods and certified laboratories is a requirement for regulatory compliance. Lykins et al. (1992) recommend that monitoring programs provide some way to respond to water quality questions from residents both with and without POE or POU systems and to assess raw water quality trends. In addition to having samples collected by an employee of the small water system, options for sample collection include contracting with a POE or POU service representative, an independent laboratory, a local health department, a circuit rider operator, or a trained community resident. An advantage of using a community resident or local representative is that these persons are familiar with the residents of the community and are likely to be better able to coordinate relatively convenient sample collection times. A disadvantage of using such a person is that community residents are likely to know the least about proper sample collection and preservation procedures, water quality tests, methods for recordkeeping, water meter reading, and proper procedures for transport or shipment of samples to an analytical laboratory. Training is necessary to enable a community resident to be an effective sample collector. Concepts related to training for sample collectors were presented by Bellen et al. (1985). To avoid duplication of travel to homes and buildings equipped with POE or POU devices, the sample collector needs to be familiar with the treatment equipment used and the treatment objectives. An ability to conduct basic troubleshooting and to service equipment is also helpful, in case problems are brought to the attention of the sample collector during sampling rounds. Monitoring of POE and POU treatment devices is problematic. When water is treated to meet MCLs or to satisfy treatment technique requirements, monitoring has to be done to verify that the water quality or treatment approach is satisfactory. From a regulatory agency perspective, monitoring of POE and POU devices is a major obstacle to acceptance. For a community consisting of 50 homes and served by a central treatment facility, regulatory compliance monitoring for most of the regulated contaminants could be done at the discharge point from the treatment plant or at the point-of-entry to the distribution system. If POE or POU devices were used instead of central treatment, the community of 50 homes would have 50 water treatment devices, any one of which might possibly malfunction or reach its capacity for effective treatment at some time. The oversight effort, both for the small water system and for the regulatory agency, is multiplied several fold in such a circumstance. The cost of monitoring every POE or POU device could be a burden on small water system customers. One approach to lowering the cost of monitoring is to sample representative households that reflect typical POE or POU installations and levels of contamination rather than sampling all households with installed systems. The costs of

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--> monitoring would decrease as a smaller percentage of the devices was monitored in a year's time, but the risks of noncompliance with an MCL would increase. Striking a balance between the risks to persons consuming water exceeding MCLs because of insufficient monitoring and the cost of analyzing numerous monitoring samples will be a challenging task for small water systems using POU or POE devices and for the regulatory agencies overseeing such systems. Regulatory Approach to POE and POU Systems The EPA (1985) has established the following conditions that must be met to ensure protection of public health when POE or POU systems are used for compliance purposes: Central control: Regardless of who owns the POE or POU system, a public water system must be responsible for operating and maintaining it. Effective monitoring: A monitoring program must be developed and approved by the state regulatory agency before POE or POU systems are installed. Such a monitoring program must ensure that the systems provide health protection equivalent to that which would be provided by central water treatment meeting all primary and secondary standards. Also, information regarding total flow treated and the physical conditions of the equipment must be documented. Effective technology: The state must require adequate certification of performance and field testing as well as design review of each type of device used. Either the state or a third party acceptable to the state can conduct the certification program. Microbiological safety: To maintain the microbiological safety of water treated with POE or POU devices, the EPA suggests that control techniques such as backwashing, disinfection, and monitoring for microbial safety be implemented. The EPA considers this an important condition because disinfection is not normally provided after POE systems. Consumer protection: Every building connected to the public water system must install POE or POU treatment and adequately maintain and monitor it. Although several states have developed regulations for the certification of POE and POU devices, California has the most extensive program for regulating the use of POE and POU systems in place of central treatment. The California action may be indicative of the approach other states will take in the future. The California Department of Health Services (DHS) does not allow the installation of POE or POU devices by community water systems unless all other available alternatives have been evaluated and found to be infeasible. The evaluation submitted to regulators must document the water quality problem or problems, alternatives pursued to correct the problem, potential for connection with an adjacent utility, comparison of POU or POE treatment versus central treatment,

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--> potential for development of new ground water sources, and potential for developing and treating a surface water source. In addition, the California DHS specifies a list of conditions that must be considered in the approval process for POE and POU devices. These conditions include utility responsibility for POE or POU ownership and maintenance, and for ongoing monitoring of contaminants, including monthly bacteriological samples. In addition, California regulations require that the POU and POE devices be either pilot tested at each individual site or that the performance of the equipment be certified in a formal testing program. Testing for certification must be conducted by a recognized testing organization and must be performed in an independent laboratory meeting laboratory accreditation requirements set forth by the California DHS. The testing must be carried out according to specified protocols accepted by the California DHS. If the equipment manufacturer makes health or safety claims regarding the ability of the device to remove specific contaminants, these claims must be verified. In addition, testing must demonstrate that the equipment will not add toxic substances to the treated water, such as by leaching from system components. The California regulations for certification of POU and POE devices draw on standards for the testing of this equipment established by the National Sanitation Foundation (NSF) International. NSF International has issued seven standards related to the testing of POE and POU devices: standard 42, which covers the ability of GAC and mechanical filtration to improve the aesthetic qualities of drinking water; standard 44, which specifies testing protocols for cation exchange units; standard 54, which provides protocols for testing the ability of GAC and mechanical filtration systems to remove contaminants posing a health hazard; standard 55, which specifies how to test UV disinfection systems; standard 58, which outlines testing requirements for reverse osmosis systems; standard 61, which details how to test for the possibility that chemicals will leach from system components into the water; and standard 62, which sets forth testing protocols for distillation systems. NSF International has a certification laboratory that can conduct a full range of physical, microbiological, radiological, inorganic, and organic analyses. The Water Quality Association (WQA) also has a certification program for POE and POU devices. However, the WQA is a trade association for POE and POU equipment manufacturers and therefore cannot provide the type of independent analysis available from NSF International (Lykins et al., 1992). Local planners considering the purchase of POE and POU devices need to be aware of this distinction when purchasing POE and POU equipment and interpret the WQA certification accordingly.

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--> Circumstances for Use of POU or POE Systems The drinking water industry and state regulatory agencies have often opposed the installation of POE or POU systems as the choice of technology to treat water and comply with drinking water regulations. Regulatory objections to these devices include the following: POU devices do not treat all the water taps in a house, posing the potential health risk of household residents drinking untreated water. Control of treatment, water quality monitoring, routine operation and maintenance, and regulatory oversight is complex because treatment is not centralized. Unless monitoring requirements are decreased from those stipulated for centralized treatment, monitoring is more costly than for centralized treatment because of the numerous individual home treatment devices that must be checked. Ensuring regulatory compliance is more difficult than with centralized treatment. Service life and efficiency of treatment units depend on source water quality, so performance can vary from household to household. Community water systems are concerned about the liability associated with entering a customer's home to monitor or service the units. Despite these concerns, a driving for the use of POU and POE treatment devices has been the cost differential. When POU devices are used, only water that is used for potable purposes is treated. If a source water is acceptable for drinking except for exceeding the standard for nitrate or fluoride, for example, treating the small number of liters per day needed for drinking and cooking might be less costly than installing a centralized treatment system that could remove nitrate or fluoride from all water used by the community. Water used to wash cars, water lawns, flush toilets, or launder clothing would not need to have nitrate or fluoride removed. Similarly, POE devices can save the cost of installing expensive new equipment in a central water treatment facility. They can also save the considerable costs of installing and maintaining water distribution mains when they are used in communities where homeowners have individual wells. As the population served by a small system increases, the monitoring, operation, and maintenance costs associated with POU and POE devices increase in direct proportion to the population. Table 3-5 shows a cost comparison for using POE versus adding a GAC treatment system to the water treatment plant for a community with between 10 and 50 households (Goodrich et al., 1992). As the table shows, when 20 or more households are involved for this example, modifying the central treatment plant is less costly than installing and maintaining POE devices in individual homes. Figures 3-11 compares the cost of installing POE systems with that of connecting homes to a central water treatment plant. As

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--> TABLE 3-5 Cost of POE versus Central Treatment for Removal of Organic Chemicals by Granular Activated Carbon   Cost ($) per Household per Year>   DBCP TCE 1,2-DCP Number of Households Central POE Central POE Central POE 10 1,325 775 1,332 815 1,356 900 15 954 775 960 815 985 900 20 760 775 766 815 790 900 25 639 775 646 815 670 900 50 380 775 385 815 410 900 NOTE: The household water usage rate is assumed to be 80 gal per-person per day, with 3.3 people per household. The POE unit includes two GAC contractors with 2 cu ft of GAC in series and a design loading of 4 gal per minute per square foot. GAC replacement is assumed to occur every 1 to 2 years. For central treatment, it was assumed that GAC postcontactors would require GAC replacement every 70 to 250 days depending on the organic contaminant removed. DBCP is dibromochloropropane; TCE is trichloroethylene; 1,2-DCP is 1,2-dichloropropane. SOURCE: Reprinted, with permission, from Goodrich et al. (1992). ©1992 by the Journal of the American Water Works Association. shown in this figure, if 20 homes are involved and the length of distribution pipe required is less than 4,000 ft. (1,200 ms), then connecting to a central treatment plant is more cost-effective than using POE devices. Use of POE and POU treatment devices to satisfy drinking water regulatory requirements may be appropriate in some instances, especially for very small systems. In some cases, POE might be the only affordable solution for a very small community with limited financial resources. However, the objections to using POE and POU treatment devices are substantial and have merit, particularly as the system size increases and the complexity of monitoring and servicing the devices increases. Using centralized water treatment should be the preferred option for very small systems, and POE or POU treatment should be considered only if centralized treatment is not possible. Bottled Water Distribution Bottled water use in the United States has increased at a rate of approximately 15 to 20 percent per year over the past 20 years (Richardson, 1991). This

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--> FIGURE 3-11 Cost of POE versus connecting to a central system. The POE device in this example is like that described in Table 3-5. The central treatment alternative assumes that a 6 x 103 m3/d (1.6 mgd) conventional plant serving 10,000 people exists nearby and can deliver water at $1.70 per 3,800 liters (1,000 gal). The example assumes that the conventional plant does not need any process modifications. The additional distribution system required is assumed to be a combination of 15- and 20-m (6- and 8-in.) ductile-iron pipes, fittings, and valves. SOURCE: Reprinted, with permission, from Goodrich et al. (1992). ©1992 by the Journal of the American Water Works Association. increase has occurred despite the high costs of bottled water: the U.S. General Accounting Office found that ''consumers may be paying as much as 300 to 1,200 times more per gallon for bottled water than for tap water because they believe it tastes better, is safe and healthy, or is free of contaminants" (Community Nutrition Institute, 1991). The majority of bottled water is purchased for aesthetic reasons rather than for quality reasons related to drinking water regulations.

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--> Some bottled water is used by necessity rather than because of personal preferences. Examples of necessary uses include water used in areas that have experienced floods, earthquakes, or hurricanes. Bottled water is commonly provided to those who cannot boil water, such as motel and hotel patrons, when a community experiences a waterborne disease outbreak. Bottled water is now recognized as an alternative water supply for emergency purposes by the Department of Interior's Emergency Water Supply Plan, the U.S. Army Corps of Engineers' Emergency Water Plan, and the EPA's National Contingency Plan under the Superfund act. In addition, the EPA rules specify that bottled water, like POU devices, may be used on a temporary basis to avoid anunreasonable risk to health or as a condition of a variance or exemption to drinking water regulations. Bottled water comes from a variety of sources, including springs, artesian wells, and even public water systems. Bottled water derived from municipal water systems may be treated with ozone and GAC to enhance its taste and odor properties before it is bottled. The Food and Drug Administration (FDA) regulates bottled water. However, the FDA regulates fewer contaminants than does the EPA under the SDWA. If bottled water were to be provided to customers of a small water system as a means of meeting EPA regulations, bottlers who use public water supplies as their sources would probably be appropriate choices to consider, as the status of compliance with EPA regulations for the source of the bottled water would be known or readily available. Distribution of bottled water is an important issue to resolve if a small system uses bottled water to comply with EPA regulations. One approach would be to have a supply available at the town hall or the water system office for water system customers to take home at no charge. Another approach would be to deliver a supply of bottled water to each household on a regular basis. In a recent American Water Works Association (AWWA) Research Foundation project, a supply of bottled water was delivered once every 2 weeks to each family participating in a study involving bottled water (R. Karlin, AWWA Research Foundation, personal communication, 1996). If more water was needed before the end of the 2 weeks, study participants called and more water was provided. Because of the logistics of providing bottled water, it is appropriate only for intermittent or short-term purposes, rather than for continuous, long-term needs. Conclusions The complexity of choosing, financing, operating, and maintaining a small water supply system cannot be overstated. Technology applications differ in their suitability for different water sources and water system sizes. Important factors in choosing a treatment technology for the small water supply system include regulatory compliance; source water quality; capital, operational, and maintenance expenses; and expertise required to operate the system.

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--> In selecting drinking water treatment technologies, small communities should keep the following considerations in mind: Small systems should apply technologies to meet requirements of the Safe Drinking Water Act only after exhausting all other possible options. Other routes to compliance include finding an alternative water source, linking with another water system, or purchasing treated water from another system. No single water treatment process can solve all water quality problems. Water systems may need to apply a sequence of technologies to meet all regulatory requirements and customer preferences. The most cost-effective way to reduce the incidence of most types of waterborne disease caused by microbial pathogens is to disinfect the water. Free chlorine is the easiest type of disinfectant for small systems to apply to meet requirements of the SDWA. However, other strategies, such as use of ozone prior to treatment followed by use of chloramine in the water distribution system, may be needed to minimize the formation of disinfection byproducts that are already or will soon be regulated. For small systems using ground water sources, the most commonly reported chemical contaminants influencing the selection of water treatment systems are nitrate, fluoride, and volatile organic compounds. Elevated nitrate and fluoride levels can be reduced with ion exchange, electrodialysis reversal, or reverse osmosis systems. Volatile organic compounds can be stripped from the water by aeration. Other types of synthetic organic compounds can be treated by adsorption on granular or powdered activated carbon. For small systems using surface water sources, treatment requirements are driven by the Surface Water Treatment Rule, which requires filtration and disinfection of the water. Membrane filtration systems may best address the variety of problems in surface water because they simultaneously remove microbial contaminants (although disinfection is still required), organic matter that can form disinfection byproducts, and, in the case of reverse osmosis, inorganic chemicals. Slow sand filtration is an appropriate treatment process for surface waters of high quality. Automated devices for monitoring small water systems can allow several small systems to share an operator, who can be better trained than a part-time operator. However, remote monitoring does not eliminate the need for routine maintenance checks. Very small water systems (those serving fewer than 500 people) may consider using point-of-use or point-of-entry treatment devices in individual homes as an alternative to centralized treatment if all other options are too costly. However, maintenance and compliance responsibilities must remain with the water supplier rather than with the individual homeowner. Developing institutional arrangements for managing these systems may be a greater challenge than finding technology that is effective for removing the contaminants of concern

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--> and may elevate the costs of these units above the costs of central treatment. In the case of POU devices, the need to enter customers' homes to service the equipment, plus the fact that these devices treat water at only one tap, may preclude their use as a long-term solution to water quality problems. Bottled water can be an acceptable short-term solution for providing drinking water of acceptable quality. However, because of the difficulties associated with distributing it and making sure consumers do not ingest the tap water, it is not an appropriate long-term solution. References AWWA (American Water Works Association). 1980. The Status of Direct Filtration. Journal of the American Water Works Association 72(7):405–411. AWWA Committee. 1992. Survey of water utility disinfection practices. Journal of the American Water Works Association 84(9):121–128. AWWA. 1995. Electrodialysis and Electrodialysis Reversal, First Edition. Denver: AWWA. AWWA Research Foundation. 1996. Internal Corrosion of Water Distribution Systems, Second Edition. Denver: AWWARF. Bauer, M. J., J. S. Colbourne, D. M. Foster, N. V. Goodman, and A. J. Rachwal. 1996. GAC enhanced slow sand filtration. Pp. 223–232 in Advances in Slow Sand Filtration and Alternative Biological Filtration, N. Graham and R. Collins, eds. New York: John Wiley & Sons. Bellamy, W. D., D. W. Hendricks, and G. S. Logsdon. 1985a. Slow sand filtration: Influences of selected process variables. Journal of the American Water Works Association 77(12):62–66. Bellamy, W. D., G. P. Silverman, D. W. Hendricks, and G. S. Logsdon. 1985b. Removing Giardia cysts with slow sand filtration. Journal of the American Water Works Association 77(2):52–60. Bellen, G., M. Anderson, and R. Gottler. 1985. Management of Point-of-Use Drinking Water Treatment Systems. Ann Arbor, Mich.: National Sanitation Foundation. Benjamin, L., R. W. Green, A. Smith, and S. Summerer. 1992. Pilot testing a limestone contractor in British Columbia. Journal of the American Water Works Association 84(5):70–79. BETZ. 1980. BETZ Handbook of Industrial Water Conditioning. Trevose, Pa.: BETZ Laboratories, Inc. Brigano, F. A., J. P. McFarland, P. E. Shanaghan, and P. Burton. 1994. Dual-stage filtration proves cost-effective. Journal of the American Water Works Association 86(5):75–88. Cheryan, M. 1986. Ultrafiltration Handbook. Lancaster, Pa.: Technomic Publishing. Cleasby, J. L. 1991. Source water quality and pretreatment options for slow sand filters. Chapter 3 in Slow Sand Filtration, G. S. Logsdon, ed. New York: American Society of Civil Engineers. Cleasby, J. L., D. J. Hilmoe, and C. J. Dimitracopoulos. 1984. Slow sand and direct in-line filtration of a surface water. Journal of the American Water Works Association 76(12):44–45. Community Nutrition Institute. 1991. FDA not enforcing rules on bottled water: GAO. Nutrition Week (April):6. Conlon, W. J. 1990. Membrane processes. Chapter 11 in Water Quality and Treatment: A Handbook of Community Water Supplies , Fourth Edition. Denver: American Water Works Association. Cullen, T. R., and R. D. Letterman. 1985. The effect of slow sand filter maintenance on water quality. Journal of the American Water Works Association 77(12):48–55. Duranceau, S. J., J. S. Taylor, and L. A. Mulford. 1992. SOC removal in a membrane softening process. Journal of the American Water Works Association 84(1):68–78.

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