Water coolers have become an essential fixture in nearly every American office. However, a recent study from California scientists raises concerns about these ubiquitous dispensers, suggesting they may harbor billions of bacteria.

Researchers at Loma Linda University examined data from 70 studies conducted over the past 20 years across five countries, including the United States and the United Kingdom. Their findings reveal that, in many instances, water dispensers contain more bacteria than the tap water they dispense. Alarmingly, soda machines were also found to be contaminated with bacteria.

Notably, some machines showed signs of bacterial growth just days after undergoing disinfection. Among the microbes detected were fecal coliform bacteria, which are associated with human and animal waste. These bacteria pose a risk of gastrointestinal illnesses, including nausea and vomiting, and in rare cases, can lead to deadly infections.

They found that water dispensers, in many cases, contained more bacteria than the tap water sources supplying them. Soda machines were also found to have bacterial contamination.

In some cases, bacterial growth emerged just days after the machines had been disinfected. 

Microbes infesting the machines included fecal coliform, bacteria linked to human and animal waste that can raise the risk of gastrointestinal illnesses such as nausea and vomiting. In rare cases, infections with the bacteria can be deadly.

Dr Ryan Sinclair, an environmental microbiology expert who was involved in the study, said: ‘Filtering out residual chlorine that’s in water makes an ideal situation for bacteria to grow. You’ve got to clean the tubes and change the filters regularly.’

Bacteria are normally not in tap water sources because of trace levels of chlorine, which kills off the microbes.

Scientists are warning that water coolers and dispensers could be contaminated with bacteria (stock image)

But in water coolers and dispensers, chlorine can be filtered out, allowing bacteria to grow, while damp surfaces on nozzles can also trigger its growth.

Staff can also fail to regularly clean or change water filters in the machines, which the experts warned could result in filters becoming a breeding ground for bacteria.

The authors said that their study aimed to boost awareness around the risks from water dispensers and to encourage regular cleaning of the machines.

Led by Dr Thomas Hile, a water quality expert at Crafton College Hills, California, the scientists said the machines should be cleaned every two to four weeks, or every week in the case of regular usage. 

In the study, published in the journal AIMS Microbiology, researchers analyzed studies on bacterial contamination in water dispensers or coolers.

For the papers that were studied, researchers had tested the inside of water coolers and their nozzles, or the point from which they dispense water, for bacteria.

The studies also looked at water dispensers that were directly connected to the tap water supply and those that have a large bottle of distilled water placed on top. 

Overall, the researchers said their study showed that the surfaces of water dispensers could become contaminated with biofilms, a slimy, protective layer made by microorganisms, which allow bacteria to proliferate and thrive.

Researchers also warned other studies had shown that soda machines could be contaminated (stock image)

Bacteria had been found growing on the machines, in some cases, just a few days after they had been cleaned (stock image)

This could happen on the outside of the machines, inside their water containers, tubes or on their nozzles used to fill bottles.

Their paper cited a study published in Italy in 1987, which found that nozzles from hot drinks vending machines had 100-fold more bacteria than other areas on the same water dispenser.

It also cited a 2020 paper from researchers in the UK, which found that inadequate cleaning of these machines may result in biofilm formation.

On soda fountains, their study cited a 2010 paper from researchers in Virginia, which found that 48 percent of the 20 self-service soda machines it sampled were contaminated with coliform bacteria, or bacteria typically found in human feces that can cause gastrointestinal illnesses.

In some cases, this included E. coli, which is a type of coliform bacteria.

Additionally, the researchers cited a study on 36 soda machines in Las Vegas found 88 percent of the soda dispensers were contaminated with coliforms.

The researchers of the new review said: ‘The presence of microbial contaminants in soda fountains should not be overlooked.

‘The lack of residual disinfectant, such as chlorine in water dispensers, allows microorganisms to regrow downstream of filtration.’

They added: ‘Unlike municipal water distribution, where residual chlorine suppresses microbial proliferation, water dispensers supply water that is typically free of disinfectant. 

‘This creates favorable conditions for microbial survival, particularly within internal tubing and dispensing outlets.’