Many people turn to commercial water dispensers believing they offer a cleaner alternative to tap water. But a new global review suggests that without regular maintenance, these machines may actually expose users to higher levels of microbial contamination than the water they are meant to improve.
The review, published in AIMS Microbiology, analyzed nearly 70 studies from around the world examining the microbiological quality of water from commercial water dispensers, including bottled water coolers, point-of-use filtration systems and beverage machines.
Across multiple countries and settings, researchers consistently found that water dispensers were more likely to contain bacteria than the municipal tap water supplying them. The problem was not the source water itself, but what happens inside the machines after filtration.
“Filtering out residual chlorine creates ideal conditions for bacteria to grow,” said Ryan Sinclair, a professor of environmental microbiology at Loma Linda University and a co-author of the review. “If internal lines, filters and nozzles aren’t cleaned frequently, biofilms can form and allow microbes to multiply.”
Biofilms are slimy layers of microorganisms that adhere to internal surfaces, especially plastic tubing and narrow spigots. Once established, they can quickly reseed bacteria into dispensed water, even shortly after disinfection. Several studies reviewed found microbial regrowth within days of cleaning.
Commonly detected organisms included coliform bacteria and Pseudomonas aeruginosa, an opportunistic pathogen that poses higher risks for older adults and people with weakened immune systems. While most healthy individuals are unlikely to become ill, the authors note that repeated exposure may increase the risk of gastrointestinal symptoms or infection in vulnerable populations.
The review also highlights a regulatory gap. In many countries, including the United States, water dispensers are not subject to the same routine microbial testing required for municipal water systems. As a result, maintenance schedules are often left to operators or vendors, with inconsistent oversight.
Based on the evidence, the authors recommend that internal system lines and dispensing outlets be disinfected every two to four weeks, and more frequently in high-use locations. They also emphasize the need for clearer regulations and routine monitoring to ensure these machines actually improve, rather than degrade, water quality.
The review did not list specific external grant funding, indicating the work was conducted as an independent academic synthesis of existing research.