Microbiological Effectiveness and Cost of Boiling to Disinfect Drinking Water in Rural Vietnam THOMAS F. CLASEN,* ,† DO HOANG THAO, ‡ SOPHIE BOISSON, † AND OLEG SHIPIN ‡ London School of Hygiene and Tropical Medicine, Keppel St., London, WC1E 7H, U.K., and WHO Collaborating Centre for Water Supply and Waste Disposal, School of Environment, Resources and Development, Asian Institute of Technology, Pathumthani, Thailand Received October 03, 2007. Revised manuscript received December 16, 2007. Accepted December 17, 2007. Despite certain shortcomings, boiling is still the most common means of treating water in the home and the benchmark against which alternative household-based disinfection and filtration methods must be measured. We assessed the microbiological effectiveness and cost of boiling among a vulnerable population relying on unimproved water sources and commonly practicing boiling as a means of disinfecting water. In a 12 week study among 50 households from a rural community in Vietnam, boiling was associated with a 97% reduction in geometric mean thermotolerant coliforms (TTCs) (p < 0.001). Despite high levels of faecal contamination in source water, 37% of stored water samples from self-reported boilers met the WHO standard for safe drinking water (0 TTC/100 mL), and 38.3% fell within the low risk category (1–10 TTC/100 mL). Nevertheless, 60.5% of stored drinking water samples were positive for TTC, with 22.2% falling into the medium risk category (11–100 TTC/100 mL). The estimated cost of wood used to boil water was US$ 0.272 per month for wood collectors and US$ 1.68 per month for wood purchasers, representing approximately 0.48% to 1.04%, respectively, of the average monthly income of participating households. Introduction Unsafe drinking water, along with poor sanitation and hygiene, are the main contributors to an estimated 4 billion cases of diarrheal disease annually, causing 1.8 million deaths, mostly among children under 5 years of age (1). By inhibiting normal consumption of foods and adsorption of nutrients, diarrheal diseases are an important cause of malnutrition, which leads to impaired physical growth (2), reduced resistance to infection (3), and potentially long-term gas- trointestinal disorders (4). Contaminated water is an im- portant contributor to other potentially waterborne diseases, including typhoid, hepatitis A and E, and poliomyelitis. An estimated 1.1 billion people lack access to improved water supplies; many more rely on piped or other improved supplies that are nevertheless microbiologically unsafe (5). Evidence has shown that treating water at the household level is effective in improving the microbiological quality of drinking water and in preventing diarrheal disease (6, 7). A variety of filtration, disinfection and other methods have emerged for treating water at the point of use (8), and the World Health Organization now endorses effective household water treatment as a means of achieving the health gains associated with safe drinking water to those not yet served by reliable piped-in water (9). Boiling or heating with fuel is perhaps the oldest means of disinfecting water at the household level (8). It is also the most widely used means of treating water in the home, with perhaps hundreds of millions of practitioners (10). If practiced correctly, boiling is also one of the most effective, killing or deactivating all classes of waterborne pathogens, including protozoan cysts that have shown resistance to chemical disinfection and viruses that are too small to be mechanically removed by microfiltration (11). Heating water to even 55 °C has been shown to kill or inactivate most pathogenic bacteria, viruses, heminths, and protozoa that are commonly water- borne (12). Moreover, while chemical disinfectants and filters can be challenged by excess turbidity and certain dissolved organics, boiling can be used effectively across a wide range of physical and chemical characteristics. In rural Kenya, pasteurization of water using a simple wax indicator to show household members when water reached 70 °C increased the number of households whose drinking water was free of coliforms from 10.7 to 43.1% and significantly reduced the incidence of severe diarrhea compared to a control group (OR 0.55, p ) 0.0016) (13). Governments, NGOs, and others have promoted the practice, both in developing countries where water is routinely of uncertain microbial quality and in developed countries when conventional water treatment fails or water supplies are interrupted due to disasters or other emergen- cies. Sources vary in the time recommended for bringing water to a boil for necessary disinfection, from 1 min (14) to 10 min (15), 20 min (16), and even 25 min (17). These longer times may have evolved from recommendations for sterilizing medical devices rather than the water itself. The WHO Guidelines for Drinking Water Quality simply recommend bringing water to a rolling boil as an indication that a disinfection temperature has been achieved (18). Despite its long history, however, boiling water presents certain disadvantages that may limit its scalability as a means of routinely treating drinking water. First, boiling is more costly than some other alternatives for treating water in the home (19), and in some cases prohibitively expensive (20). Second, more than half of the world’s population relies chiefly on wood, charcoal and other biomass for their energy supplies (21). The procurement of these fuels represents a substantial commitment of time and energy, primarily for women and girls, and may detract from other productive and potentially health-promoting activities (22). Third, boiling can be an important cause of other health hazards, including respiratory infections associated with poor indoor air quality (23) and burns, especially among young children (24 ,25). Fourth, depending on the fuel used, boiling may be environmentally unsustainable and contribute to greenhouse gases. Finally, there is an increasing body of evidence suggesting that as actually practiced in the home, boiling and storing water often does not yield microbiologically safe drinking water. Once the water begins to cool, it is immediately vulnerable to recontamination from hands and utensils since it contains no residual disinfectant and is often stored in open vessels without a tap (26 ,27). Recent studies have shown that the stored drinking water in the homes of families who report * Corresponding author: phone (+44) 020 7927 2916; fax (+44) 020 7636 7842; e-mail: thomas.clasen@lshtm.ac.uk. † London School of Hygiene and Tropical Medicine. ‡ Asian Institute of Technology. Environ. Sci. Technol. XXXX, xxx, 000–000 10.1021/es7024802 CCC: $37.00  XXXX American Chemical Society VOL. xxx, NO. xx, XXXX / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 A Published on Web 02/05/2008