Water dispensers can contain more bacteria than tap water

Water dispensers can contain more bacteria than tap water

A comprehensive review shows how biofilms and poor maintenance can affect filtration systems, refuting the notion that water coolers are always a safer choice than tap water.

Study: Microbiological quality of drinking water from water dispensers. Photo credit: PeopleImages/Shutterstock.com

Despite their claims, water dispensers (WDs) are not always free from microbial contamination and in many cases can have microbial loads comparable to those in tap water, raising concerns about public health and the need for better maintenance. Recently, researchers conducted a comprehensive investigation to evaluate microbial contamination in water dispenser machines and examine their potential health effects. This review was published inOBJECTIVES Microbiology.

In this review, published literature was analyzed to assess microbial contamination in WDs, water quality, common contaminants, and health effects. The authors obtained all relevant documents from PubMed, EBSCO and Google Scholar and summarized evidence from approximately 70 studies conducted in multiple countries and settings.

Are water bottles or water dispensers safer than tap water?

Access to clean drinking water is a basic human right and essential to public health. Despite the rigorous treatment of public water systems, including coagulation, flocculation, sedimentation, filtration and disinfection, consumers are increasingly turning to alternatives such as bottled water and WD machines in search of perceived health benefits, convenience and better taste.

WDs, commonly known as water coolers, dispense drinking water and are classified as point-of-use systems (POU) and bottled WDs. POU systems connect directly to tap water and bottled WDs use replaceable bottles. Typically, WD machines feature filtration technologies such as reverse osmosis, carbon filtration and UV sterilization to purify water and remove unwanted tastes or odors.

Despite these filtering efforts, sporadic contamination in WD systems has been reported in many studies reviewed, raising concerns about microbial contamination originating from the donors themselves. Such contamination can increase the risk of waterborne disease, particularly for vulnerable populations. Comparative studies have often found WDs to be more contaminated than the tap water from which they come, and water quality often deteriorates over time with regular use.

Compared to tap water samples, scientists have found approximately 1.2 times higher levels of bacterial contamination in carbon filters from POU devices. These bacterial contaminants tended to re-grow in WDs even after treatment and rinsing. Although most research recommends regular maintenance and cleaning, microbial infestation often recurs within a few days, challenging the assumption that well-maintained mobile devices are consistently free of microbes.

The researchers identified biofilms, defined as structured microbial communities that build up in machines and continually release planktonic cells and byproducts into the water, as the primary source of contamination. Several international studies conducted in Turkey, Thailand, Iran, Canada, Italy and Malaysia found that in many cases WDs were more contaminated than their tap water sources. In these studies, it was observed that the number of heterotrophs and aerobic bacteria in dispensers was higher than in tap water.Pseudomonas aeruginosawas also found in WD systems.

Overall, WDs are not necessarily safer than tap water, and their safety depends heavily on system design, maintenance practices, and frequency of use, with regular maintenance remaining essential to reduce microbial colonization and regrowth.

Assessment of the quality of drinking water

The U.S. Environmental Protection Agency (EPA) uses microbial indicators, including fecal indicator bacteria (FIB) and coliform bacteria, to assess drinking water quality and regulatory compliance. Total coliforms are used as indicator organisms that can indicate fecal contamination or system integrity failures, and their presence can indicate the possible presence of pathogens, such as:Salmonella,ShigellaAndVibrio cholerae. Municipal water districts use coliform bacteria to measure treatment efficiency and distribution system integrity.

It was reported that about 20% of water samples in the US and 80% of water vending machines (WVMs) in Malaysia were contaminated with coliform bacteria due to filter failure.Pseudomonas aeruginosawas considered as a water quality indicator due to its serious health impacts, particularly for immunocompromised individuals.

Heterotrophic bacteria (HPC), which are classified as oligotrophic or opportunistic microorganisms, provide information about the overall microbiological quality of drinking water. The EPA recommended that HPC bacteria not exceed 500 CFU/mL, primarily to limit interference with coliform detection, although the World Health Organization (WHO) stated that coliform testing was a better indicator. Despite ongoing debate about their reliability as direct health risk indicators, EPA and water regulators worldwide continue to use HPCs as complementary indicators of microbial water quality.

Health effects of WD contamination

Studies conducted in Sweden and other Nordic countries have linked drinking water contamination to gastrointestinal illnesses and water-related outbreaks. Studies on drinks machines have shown that 17% of bacteria, includingChryseobacterium meningosepticum,Klebsiella,Staphylococci,Stenotrophomonas,CandidaAndSerratiawere opportunists who can cause gastrointestinal infections, especially in immunocompromised people.

Colonized biofilms in plumbing fixtures can serve as a reservoir for microorganisms associated with endocarditis, folliculitis, keratitis, cystic fibrosis, osteomyelitis, and septicemia. Opportunistic pathogens generally cause infection when the host's immunity is weakened.

Waterborne bacteria pose an increased health risk to children, the elderly and the immunocompromised. Previous research found that 23% of Malaysia's WVMs have a portPseudomonas aeruginosawhich permanently colonizes WDs through biofilm formation. Contaminated drinking water dispensers are also considered possible sourcesPseudomonas fluorescensin the hospital area.

Several studies have suggested that under certain exposure conditions, HPC bacteria may be more harmful than previously thought. Researchers have reported elevated HPCs in WDs, including 62% of Iranian samples, 100% of US samples, with 73% above 500 CFU/mL, 32% of US WVMs, 84% of UK WVMs, and 87% of Brazilian samples exceeding the 500 CFU/mL threshold.

HPCs above the recommended limits indicate that WDs may serve as potential breeding grounds for bacteria, including pathogenic microorganisms, which can have serious impacts on public health, especially if monitoring and maintenance are inadequate.

Recommendations for improving drinking water quality

To improve water quality and reduce microbial contamination, the authors recommend implementing measures that inhibit biofilm formation, such as: B. internal system lines made of biofilm-resistant materials or coatings with nanoparticles that prevent the adhesion and growth of bacteria.

The introduction of new technologies should be accompanied by compliance with regulatory safety standards, long-term stability testing and certification to confirm that harmful nanoparticle migration does not occur during operation. Additionally, regular disinfection protocols, such as the application of hydrogen peroxide, could provide a short-term but effective reduction in microbial populations in microfilter dispensers.

Regular maintenance, routine cleaning and user hygiene practices are critical to maintaining water quality. Without consistent maintenance, even systems equipped with advanced filtration technologies are vulnerable to contamination, underscoring the authors' conclusion that technological upgrades alone are not enough without sustained monitoring and maintenance.

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