Water that comes straight from natural sources, dubbed “raw water,” is gaining popularity. Raw water advocates reject public water supplies, including tap water, because they don’t enjoy the taste or believe it’s unsafe and depleted of vital minerals.

On the surface, raw water might seem alluring – the natural surroundings may look beautiful, and the water may look clean and taste refreshing. But unlike tap or commercially bottled water, raw water is not evaluated for safety. This leaves the people who drink it vulnerable to infectious microbes or potentially other toxic contaminants.

I’m a microbiology researcher studying infectious diseases. From a public health perspective, clarifying misconceptions about tap water and the health hazards of raw water can protect consumers and curtail the spread of infectious diseases.

A short history of public drinking water

Archaeological evidence suggests that humans have long associated dirty water with negative health outcomes. As early as 1500 BCE, ancient Egyptians added a binding agent to their water to clump contaminants together for easy removal.

Two major developments in the mid-1800s showed why impure water is dangerous. First, physician John Snow traced a deadly cholera outbreak to contaminated water from London’s Broad Street pump. Second, Louis Pasteur advanced the germ theory of disease, which postulated that microbes can cause illness. Pasteur established that consumable liquids like raw water and milk can harbor disease-causing pathogens.

These discoveries paved the way for large-scale infrastructure projects in the 20th century to ensure the public water supply is safe.

Today, the process of cleaning water begins with the same steps employed by the ancient Egyptians, followed by extensive filtration to get rid of debris as well as most germs and chemicals. Chlorine is added to kill lingering pathogens, including those that may reside in the service pipes carrying the water to the faucet. Beginning in the 1940s, a small amount of fluoride was added as an inexpensive, safe and effective means to improve dental health.

The cleanliness and fluoridation of the water supply has dramatically reduced infectious disease and cavities, and has been heralded as one of the 20th century’s greatest public health achievements.

Is raw water healthier than tap water?

People who champion raw water claim it has health benefits, such as essential minerals and beneficial bacteria called probiotics, that are stripped from tap water. Let’s unpack each of these claims.

Water dissolves bits of soil and rock at its source; therefore, its mineral content depends on the local geology. Areas with a lot of limestone, like the Midwest, have water that is higher in calcium. Water from deeper in the ground may have higher mineral content since it passes through more rock on its way to the surface.

The idea that tap water is depleted of essential minerals is not true, as these nutrients are too small to be excluded by the filtration process. Test kits can determine the mineral content of your water, and if you find it lacking, mineral supplements can be added. Experts suggest, however, that most minerals you need come from your diet, not water.

Some also claim that raw water contains probiotics that are removed from tap water. The amount of probiotics in water would also vary by location, and the notion that health-promoting bacteria reside in raw water has not been proved.

There are no studies associating raw water with any health benefit. Anecdotal claims about smoother skin or increased energy are likely to be placebo effects. Even the idea that raw water tastes better might be more psychological than physiological – a 2018 study showed that most people preferred tap water over bottled water in a blind taste test.

Risks of drinking raw water

Raw water carries the risk of serious gastrointestinal infection from a wide variety of pathogens.

Water-borne viruses include rotavirus and norovirus, which cause rapid-onset diarrhea and vomiting, and hepatitis A, which infects the liver. Bacteria such as E. coli and Salmonella, or parasites like Cryptosporidium and Giardia, also cause severe diarrhea that can lead to dangerous levels of dehydration. Toxoplasma gondii can also lurk in raw water and can cause miscarriage or birth defects if consumed during pregnancy.

Carriers of diarrheal infections can transmit them to others if they swim in public pools or fail to properly wash their hands before touching others or preparing food. Norovirus is particularly durable and can survive on surfaces for days, increasing chances of it infecting someone else.

Raw water can also contain algae that release toxins causing abdominal issues and damage to the brain and nervous system.

Cholera, dysentery and typhoid fever are no longer health burdens in the U.S. thanks to a robust water treatment system. But areas of the world lacking this privilege suffer high child mortality and widespread diarrheal diseases.

How safe is tap water in the US?

Tap water in the U.S. is among the safest to drink in the world. The Biden administration took steps to further improve it, including funding to replace lead pipes and new rules to monitor forever chemicals like perfluoroalkyl and polyfluoroalkyl substances, or PFAS, which have been linked to cancer and developmental disorders.

Importantly, raw water is not necessarily free from lead, arsenic, pesticides or industrial contaminants. Raw water sources are not reliably monitored by experts, so it is difficult to say which ones pose less risk. In addition, the water may be acceptably safe one day, but not on another. For example, soil runoff from a storm could introduce new germs or pollutants into the area.

The Environmental Protection Agency routinely screens for nearly 100 contaminants to ensure tap water is safe. In contrast, raw water remains untested, unregulated and untreated, leaving its safety to drink in question. In terms of risks and benefits, there are no demonstrated health benefits from drinking raw water, but clear evidence that you may be exposing yourself to harmful infectious and toxic contaminants.

Bill Sullivan receives funding from the National Institutes of Health.