An unusual trend has been gaining steam since late 2017. It’s called raw water, and its fans say it’s healthier than tap water, more natural, even probiotic. Raw water has mostly taken off in California and in affluent areas of the East Coast, among the same demographics who might go in for raw food diets or juicing. And some customers are willing to pay a premium to call themselves raw-water drinkers.

Of course, “raw water” is not a new thing. People have collected water directly from roadside and trailside springs for centuries, and specific springs have long been reputed to offer health-promoting properties. Many bottled water brands tout their water’s origin at some of these same springs, though bottled water is required to be tested and treated, if necessary, to bring it within federal and state water quality standards.

So, is “raw water” just re-branded bottled water? Or is this trend actually unsafe?

To answer this, it’s important to distinguish between different types of untreated water. Water safety depends on both the source – surface water, groundwater, or rainwater – and on what the water has been in contact with on its way from the source to the consumer. For all sources, water testing is very important to ensure safety.

Surface water and groundwater

Collecting untreated surface water (like the water in streams, rivers and lakes) for drinking can certainly make you sick. E. coli, Cryptosporidium, Shigella and hepatitis A virus are just a few of the infectious agents frequently found in untreated water located near human residences. Industrial and pesticide contamination are also concerns. Runoff from farms, factories, roads and cities easily enters surface bodies of water.

Clearly, in today’s world, it’s extremely difficult to find a stream or lake that’s untouched by human activity. But when it comes to microbes, even that bubbling mountain stream is likely not as clean as it looks. The parasite Giardia lamblia is shed in wild animal droppings and can survive for several months in a wilderness stream. This parasite can make you miserable for six weeks or more.

In contrast with untreated surface water, groundwater – in its original state deep under the earth’s surface – is often safe without treatment. Groundwater supplies are built up over time as water seeps into the earth through layers of soil, sand, silt and clay. Microbes and many organic contaminants get caught in tiny pores and stick to particles as the water passes through. Thus, deep ground water is naturally filtered and is typically free of microbes or even viruses.

Deep wells and water collection at natural springs are both ways of accessing this potentially safer water resource. But there are some major caveats: groundwater quality ranges widely among regions. Contaminants in some groundwater supplies can include industrial chemicals, petroleum, natural chemical or mineral contaminants like arsenic, and bad-tasting components like sulfur. In some areas, very high natural levels of fluoride exist – much higher than the levels added to tap water that some raw water drinkers are intent on avoiding. And groundwater can be contaminated near the surface or on its way to the bottling spot.

All this means testing is necessary. Over 15 million Americans access groundwater through private wells, and the CDC recommends that these homeowners have their wells tested at least yearly for both pathogens and pollutants. Many municipal water supplies originate as groundwater, too, but only after in-depth testing and treatment.

What about probiotic claims?

One of the biggest selling points for some raw water aficionados is the idea that “raw water” is probiotic or “alive,” and that it’s healthier to consume products that contain microbes. But there’s a huge difference between the microbes in probiotic foods and the microbes in untreated water. In yogurt and properly fermented food, benign microbes outcompete and suppress harmful ones. In drinking water, on the other hand, the presence of bacteria and other life forms is not a positive as there’s no fermentation process to suppress dangerous organisms.

Looking beyond the hype, raw water appears to be just another incarnation of bottled water, something the environmentally-concerned public is turning away from. The environmental costs of its transport and bottling are likely similar to those of traditional bottled water. The cost to the planet might be even higher when you consider that some customers pay to have this “super-premium” water shipped across the country.

Raw water that is advertised as probiotic could be worse than a waste of money and resources, though. If it’s not properly tested, there’s no way to know what you’re getting.