Drinking water quality concerns and water vending machines.

Drinking water quality remains a vital public health concern to regulators and consumers alike (1-3). The Science Advisory Board, established by Congress in 1978 to advise the U.S. Environmental Protection Agency (EPA) and Congressional committees on environmental matters has classified contaminants in drinking water as a serious risk to human health (4). A recent health department survey of several hundred residents from a midwestern county found that consumers ranked drinking water quality as second in importance only to solid waste disposal among a variety of environmental health issues (5). Though often exaggerated in media reports, evidence of actual and potential risks to human health from contaminated drinking water is widespread. These risks involve an expanding assortment of microbiological, chemical, and radiological contaminants.

This article reviews some of the contemporary concerns regarding drinking water quality and the evolution of water vending machines, which can be viewed as one reaction to negative public perceptions about the quality of our tap water. The article also discusses the current treatment provided in water vending machines and describes a national certification program for their design and construction.

Microbiological Concerns

While improved methods of water purification and more comprehensive monitoring have significantly reduced the number of cases of waterborne disease in the United States, periodic outbreaks, sometimes dramatic, continue to occur in both public and private systems. In fact, 291 waterborne disease outbreaks were reported in the U.S. between 1981 and 1990 (3). The most commonly identified pathogen in waterborne outbreaks is Giardia lamblia, a flagellated protozoan that can damage the microvillous lining of the upper small intestine (6, 7). Fifty-five percent of the outbreaks of giardiasis between 1965 and 1985 occurred in community water systems, usually due to inadequate disinfection, even though turbidity and coliform concentrations were often within prescribed limits (7). Concerns about waterborne giardiasis were serious enough for the EPA to promulgate the Surface Water Treatment Rule (SWTR) in 1989 under the authority of the 1986 Safe Drinking Water Act Amendments. The rule mandates that public water systems using surface water be treated to effect a 99.9% reduction in Giardia cysts (8). The EPA has also recommended that populations served by these systems should have a risk of Giardia infection no greater than 1 case per 10,000 persons per year (8). While it is expected that this policy will further reduce the risk of giardiasis, LeChevallier, Norton, and Lee (9) have demonstrated theoretically and empirically that the SWTR will not ensure that treated waters are free of Giardia cysts, nor that the risk of infection will not exceed EPA's objective. It is also interesting to note that at least one recent epidemiologic study has suggested that more than a third of the reported waterborne cases of gastrointestinal illness may be due to consuming water that meets applicable drinking water standards (10).

Another current microbiological concern in drinking water is Cryptosporidium, a newly recognized human parasite that causes cryptosporidiosis. Outbreaks of this waterborne disease have been reported in public water systems in both the United States and the United Kingdom (3, 11). One of the most recent episodes occurred in Milwaukee, Wisconsin in April 1993, where an estimated 300,000 people became ill (12). This outbreak immediately prompted proposed legislation to establish a multi-billion dollar revolving fund that would allow states to issue loans for constructing or improving water treatment plants (12). This is just one indication of the impact water quality problems have on Congress.

Cryptosporidium infection is especially serious if contracted by AIDS patients or others with immune suppressed systems, since there is no effective drug therapy for the disease (3). As with Giardia, LeChevallier, Norton, and Lee (9) have demonstrated that compliance with the SWTR will not necessarily ensure that treated waters are free of the oocysts of Cryptosporidium. Other contemporary microbiological health concerns in drinking water include Legionella, viruses, and E. coli, hemorrhagic serotype 0157:H7, which can cause bloody diarrhea and potentially fatal hemolytic-uremic syndrome (3). As the foregoing indicates, microbiological contamination of drinking water is still a serious public health risk despite recent advances in water treatment and regulation (13).

Chemical Concerns

The number of inorganic and organic chemicals regulated or proposed for regulation under the Safe Drinking Water Act has more than doubled in recent years (14, 15). These include a variety of volatile organic chemicals, such as trichloroethylene and carbon tetrachloride; synthetic organic chemicals, including many pesticides and herbicides; and trace metals and other inorganics, such as asbestos and nitrates. Two of the more publicized chemical concerns with drinking water include lead contamination and the formation of potentially toxic disinfection by-products (DBPs).

Lead is a cumulative poison, and increasingly lower body burdens of lead have been associated with potentially serious neurologic effects in young children, including decreased learning ability and behavioral changes (16). Recent news reports of apparently widespread lead contamination in public water supplies above the EPA action level of 15 ppb have served to foster public apprehension about this important public health hazard (17).

Lead contamination in drinking water supplies typically results from the leaching of lead from plumbing connections between water distribution mains and households or from the household plumbing itself (18). For these reasons, the 1986 Safe Drinking Water Amendments prohibited the use of lead pipes, solder, and flux in plumbing connected to a public water system (19). "Lead free," as defined in the act, means no more than 0.2% lead in solders and flux and no more than 8% lead in pipes and pipe fittings (19). Most of the serious lead contamination problems appear to be associated with waters high in corrosivity, especially where these waters are distributed to older homes using lead pipes or to relatively newer homes where copper pipes have been joined with lead-based solder (18). Contact time is another important variable (20), and those with potential lead contamination in their water systems are usually advised to flush water lines before drinking, especially when the water has not been run for several hours, or to seek additional treatment or an alternative drinking water source. Trihalomethanes (THMs), such as chloroform and bromoform, formed primarily by the reaction of chlorine with naturally-occurring humic and fulvic acids, have been studied for their cancer-producing potential for almost 20 years (21). In fact, the threat of potential cancer from these and related organic substances found in chlorinated drinking water was at least partially responsible for the passage of the original Safe Drinking Water Act in 1974 (22, 14). While the chlorination DBPs-cancer connection is still considered inconclusive, concerns over DBPs will increase as alternative disinfectants continue to be tested and used in drinking water supplies. According to the American Water Works Association: "The issue of DPBs, many of which are still unidentified and whose toxicology is largely unknown, is compounded by the need to weigh the risks from these contaminants against those from waterborne microorganisms, which could flourish if disinfection is lessened. Risk assessment of this kind is hampered by inadequate data," (23, p. 43).

Radiological Concerns

Radiological contaminants in drinking water often result from leaching of naturally-occurring radionuclides in geologic structures into groundwater supplies. Radium-226 and 228, for example, are relatively common in deep well water in the southeastern U.S., New England, Texas, Iowa, Illinois, Utah, and Idaho (24). The chief health concern from radium ingestion is bone cancer based on studies of radium dial painters (25). Radium is also a risk factor for leukemia, although the magnitude of the risk from low levels in drinking water is debatable (25). Recently, EPA proposed less restrictive standards for Radium-226 and 228 in drinking water (15), which some believe reflect more economic than public health considerations. Radon is also the subject of proposed regulation under the Safe Drinking Water Act (15), although there is some controversy about the rationale behind the proposed maximum contaminant level of 300 piC/L (3). From the viewpoint of some consumer advocacy groups excess radioactivity in drinking water in any form is a serious public health issue, and anecdotal data seem to suggest that in areas where excess levels have been detected many consumers have altered their drinking water habits.

Consumer Demand for Tap Water Alternatives

Concerns about the health effects of contaminants in drinking water only partially explain the increase in consumer demand for bottled water, vended drinking water, and residential water treatment units. Consumers are also concerned about the aesthetic quality of their water, especially those aspects related to taste, odor, and appearance (26, 27). These factors, along with media hyperbole and aggressive marketing, begin to explain the evolution and growth of industries producing alternatives to tap water.

The water vending industry is a case in point. According to the Beverage Marketing Corporation (BMC) in its June 1991 edition of Bottled Water in the United States, water vending sales grew over 60% from 1988 to 1990 to a figure of $57,100,000. The BMC estimates that continued growth will average 8% per year for the period 1991-95 and 7% each year thereafter. According to Soost (28), water vending machines offer retail outlets significant advantages over bottled water. These include a reduced need to order, store, and stock valuable shelf space with bulky and low profit-generating bottled water and an improved profit margin. Soost (28) sees consumer demand for vended water as a result of cost savings (vended water prices are often 50% to 60% less than bottled water), relative convenience, perceived quality of the product, concerns about health, and increased environmental consciousness (customers can reuse their containers, thus reducing potential waste possible with bottled water containers). Highest demand for vended water appears to be among Hispanic and Asian populations (26), and the elderly, especially in warmer climates like California, Arizona, and Florida.

Water Vending Machines

Surprisingly, water vending machines are not a new phenomenon. As early as 215 B.C. sacrificial water was vended from a table top dispenser (29). It was over 2,000 years later, however, in 1908 before another "water vending machine" appeared on the scene. This time the consumer purchased a small individual paper cup from a dispenser and filled it with drinking water from an adjacent reservoir. This was the invention of the "Dixie Cup," whose manufacturers believed it would not sell unless the customer was able to use it (29). It was not until 1976, however, that the first practical water vending machine was designed and placed into use, and it was not until the early 1980s that water vending became a viable industry. Today, water vending machines are found in three basic types of installation. Most are self-contained, freestanding floor models located either inside or in front of a grocery store, convenience mart, or other retail outlet. Some water vending machines are installed on counter tops, usually adjacent to soft drink, coffee, and other beverage dispensing equipment. More recently, some water vending machines are being designed so that the treatment components are located in a remote area of the facility (often a storeroom), while a smaller dispensing unit is located on a counter top in the sales area of the store. In terms of water treatment, most water vending machines provide one or more levels of purification. Filtration-only machines provide the most basic level of treatment as depicted in Figure 3. These machines are essentially designed to reduce tastes, odors, and turbidity of the source water, which should be from an approved water system. Other machines may contain additional treatment devices to reduce high concentrations of total dissolved solids (TDS) to more palatable levels or to produce "purified water," which among other requirements, must have a TDS concentration no greater than 10 ppm (30). Many water vending machines provide more than one selection of water in the same machine (e.g., filtered-only water and purified water).

Depending on the quality of the source water, a water vending machine may begin the treatment process with a mechanical filter to remove sediment and residue. This is usually followed by activated carbon filtration and often a second mechanical filter to remove carbon fines extracted from the carbon filter. This so-called "prefiltration" process, which includes these or other filtration steps, normally uses filters with media pore sizes ranging from 1 to 20 microns. Activated carbon filtration is effective in adsorbing a wide variety of organic compounds, including those that can impart taste, odor, and color to the water, or those that may be potentially carcinogenic, such as THMs or other volatile organics (31). The carbon medium may be in block or granular form, and the longer the contact time, the greater the treatment. When the carbon adsorption capacity is exhausted, the filter must be replaced or the medium must be regenerated. Carbon filters are also used to remove or reduce chlorine, which can otherwise damage reverse osmosis (RO) membranes (31).

The RO process, which normally follows prefiltration in the treatment sequence where TDS reduction is desired, receives feed water under pressure at one end of its semipermeable membrane. The water is essentially forced through the membrane one drop at a time. As the water passes through the membrane, contaminants (dissolved and suspended solids) are left behind in the "reject" water, which can be either returned to the RO membrane for further treatment or, as is more common, discharged to drainage. Reverse osmosis systems are effective in reducing TDS; metals, such as arsenic, cadmium, copper, lead, and sodium; nitrates; asbestos; radium; Giardia cysts; and bacteria (31, 24). The effectiveness of the membrane depends upon several factors, including its age, the type of contaminants, and the concentration of solids in the feed water.

If a water vending machine produces "purified" water, the drinking water processed by the RO may pass through a deionization tank for further TDS reduction to a level no greater than 10 ppm. Machines utilizing RO treatment will have an internal storage tank, since the RO membrane requires considerable time to produce reduced TDS water. The storage tanks may be either pressurized or non-pressurized.

Disinfection is the last step in the treatment process before the water is dispensed into a customer's container. Disinfection in water vending machines is usually accomplished by exposing the water to ultraviolet (UV) radiation. A UV lamp is similar to a fluorescent one except that it uses a low-pressure mercury vapor to produce the desired UV wavelength (254 nanometers). Since most materials do not efficiently transmit ultraviolet light, a special quartz glass is used to encase the lamps. The quartz glass allows about 93% of emitted ultraviolet light to pass into the water (32).

When exposed to UV light, microorganisms are destroyed because the UV scrambles their DNA structure, which interferes with cell reproduction (32). Radiation dosage, exposure time, and water quality are just a few of the factors that must be considered in effective germicidal treatment (32). Normally, 13,000 microwatt-seconds per square centimeter at a wavelength of 254 nanometers is sufficient for effective disinfection in water vending machines (30).

Some water vending machines use ozonation as a means of disinfection. In this process, ozone is injected into the water immediately prior to dispensing. An ozone concentration of 0.5 ppm is recommended by the International Bottled Water Association to ensure effective germicidal action. Unlike UV, ozone causes cell lysing (33). A potential limitation of ozone disinfection is that it imparts an odor to the drinking water. Since the half-life of ozone is short, however (typically less than 30 minutes), this should not be considered a significant problem.

The NAMA Water Vending Machine Evaluation Program

With the proliferation of water vending machines in the United States, some measures of quality control are essential. While local and state health authorities have primary responsibility for enacting and enforcing minimum public health and safety standards for the installation, operation, and maintenance of water vending machines in the field, it would also seem important to have a national standard for their design and construction. Fortunately, such a standard exists.

In 1957, the National Automatic Merchandising Association (NAMA) established the Automatic Merchandising Health-Industry Council (AMHIC) as an independent advisory group. AMHIC's health members represent professional associations and local, state, and federal regulatory agencies, while its industry members represent vending machine operators and manufacturers. The Council's original task was to establish a voluntary program for the evaluation of food and beverage vending machines as defined by the U.S. Public Health Service Ordinance and Code, The Vending of Food and Beverages. As a result of its activities, the Council developed the NAMA Standard for the Sanitary Design and Construction of Food and Beverage Vending Machines, which became effective in 1961. Ten subsequent revisions have appeared between 1966 and 1990 (30), including the addition of a section on standard water vending machines in 1984. When a vending machine meets the requirements of the Standard, a "Letter of Compliance," identifying the machine by manufacturer, model number, type of product, special qualifications, and date of certification, is issued by an independent public health consultant who conducts the evaluation. Reevaluations are conducted annually to assure machines continue to be manufactured in compliance with the Standard.

Many regulatory agencies rely on the NAMA Evaluation Program as a means of identifying machines that have been manufactured in accordance with nationally accepted public health standards. States, such as California, Ohio, and Georgia, require that all food and beverage vending machines, including water vending machines, carry the NAMA Service Mark, which indicates compliance with the Standard. In 1992 there were 22 manufacturers of water vending machines participating in the voluntary NAMA certification program.

The NAMA Standard defines a water vending machine as "a water-connected vending machine designed to dispense drinking water, purified and/or other water products." (30, p. 4). Drinking water, as defined by NAMA, is that "which has been disinfected and processed by a water vending machine to reduce or remove turbidity, odors and off-tastes." (30, p. 2). Purified water is defined as that "produced by a vending machine through distillation, ion-exchange, reverse osmosis, or other processes." (30, p. 3). In all cases, NAMA requires that water vending machines be connected to approved water systems only. Furthermore, drinking water machines must meet all applicable requirements of the EPA Primary Drinking Water Standards as well as secondary guidelines suggested by EPA, while purified water machines must meet the standards of the U.S. Pharmacopoeia (30).

A few examples of the many requirements for water vending machines under the NAMA Standard underscore the comprehensive nature of this voluntary certification program:

1. Filtration-only machines must be designed to be connected to potable water systems containing 500 ppm or less of TDS, since these machines do not reduce TDS concentrations and because 500 ppm is the TDS requirement under the Secondary Drinking Water Guidelines.

2. Unless a water vending machine is equipped with an inlet air gap, it must contain a vacuum breaker, reduced pressure zone device, double check valve, or other effective backflow prevention device upstream from the first processing component so as to reduce the possibility of backsiphonage or backflow into the approved source water.

3. The intensity of the UV lamp used for disinfection must be designed to be automatically or manually monitored to assure it does not fall below the pre-established standard of 13,000 microwatt-seconds per square centimeter at 254 nanometers wavelength. The machine must be designed to inactivate the vend mechanism if the UV light is missing, burns out, fractures, or falls below the required dosage.

4. The water vending machine cabinet, vending stage, and interior must be designed and constructed to facilitate routine cleaning and maintenance and to minimize the entrance or collection of moisture, dust, or vectors.

5. All water-contact parts, surfaces, and media, including recommended replacements, must comply with FDA standards (21 CFR, Parts 170-189, Food Additives Amendment), or be generally recognized as safe (GRAS) as provided in 21 CFR, Part 182.

6. Where process water is collected within the machine for discharge to an outside drain, the point of discharge from the processing unit must be at least 2 inches above the rim of the retention vessel. Additionally, the waste line from the machine must be air-gapped.

7. Sensors and/or controls must be provided that will inactivate the machine in the event of failure of any process or function that would result in water quality less than claimed (e.g., purified water) or cause waste container overflow. Machine inactivation is not required if an automatic recycling or switching mode is used to reprocess water that is of inferior quality.

8. Performance test data must be supplied showing the treatment effectiveness of all water treatment devices at the proposed operating specifications.

9. A copy of printed sanitation and servicing procedures must accompany each machine, and, at a minimum, must include machine installation procedures; step-by-step instructions for in-place cleaning and sanitation; recommended schedules for servicing and replacing components with finite effectiveness; troubleshooting guidelines for isolating water quality problems; proper control settings to maintain the quality of product waters; and a recommended schedule for testing the products for conductivity, taste, odor, turbidity, and microbiological quality.

10. To facilitate cleaning under and around a water vending machine, the cabinet must be mounted on legs, casters, etc., be easily movable by one person, or be permanently sealed to the floor or counter.

11. The vending stage must be protected by a self-closing door or panel unless the stage is designed with a mechanism that makes the dispensing nozzles inaccessible when the machine is not vending and otherwise minimizes vector entry into the machine.

12. Product waters from representative machines in production must be sampled annually to assure compliance with applicable water quality standards and to demonstrate the effectiveness of the machine's treatment processes.

A more detailed description of these and other NAMA requirements for water vending machines is available from the National Automatic Merchandising Association in Chicago or in the Standard itself (30).

Summary and Conclusions

Concerns about drinking water quality in the U.S. have provided an impetus to industries involved in the development of tap water alternatives. Water vending machines are a case in point. For some consumers, the water dispensed from vending machines is an attractive alternative to residential tap water which may be considered objectionable for aesthetic or other reasons. From a public health point of view, water vending machines should be considered acceptable water treatment and delivery devices when connected to an approved, potable water supply and when they are properly designed, manufactured, installed, and serviced. Certification programs like that provided by NAMA in concert with local and state public health inspection programs will go a long way to ensure that water vending machines provide what they claim--safe, clean, and aesthetically-pleasing water.

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David Z. McSwane, H.S.D., Associate Professor, School of Public and Environmental Affairs, Indiana University, Indianapolis, IN 46202