Tabletop filters can remove substances from tap water, but are they really necessary and can they cause unintended harm?
Given the choice, Shima Chin-Si avoids drinking water directly from the tap.
Her refrigerator at home in Northwich, UK, where she lives with her young family, has a built-in water dispenser connected to a filter.
When he is out of the house, he always has a reliable "self-cleaning" water bottle at hand, which sterilizes the water with an ultraviolet chip in its cap.
"Filtered water just tastes better
"I can smell the chemicals in the tap water, and by God I can taste them," says Chin-Si.
To some people, that claim makes her a freak, even to her own husband, who once performed a "blind test" on her (turns out she really can tell the difference between filtered and unfiltered tap water).
But it turns out that Chin-Si is not alone in such attitudes.
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When the nonprofit Environmental Working Group surveyed 2.800 people living across America, half said that "tap water" was unsafe to drink, and almost 35 percent of them filtered their own water.
Similarly, based on a 2023 survey of more than 500 people in the UK by Swedish filter company Tapwater, 42 percent of them "don't trust tap water or don't like its taste".
A quarter of respondents believed their tap water was not clean, with contaminants, chemicals and bacteria as the main reasons for concern.
As a result, more than half of Londoners (54 percent) said they use a water filter.
Water filters seem to be at the peak of popularity right now - especially in North America, Europe and China.
In 2022, the value of the global water purifier market it is estimated at 30 billion dollars, and it is expected to grow by more than seven percent by 2030.
Proponents claim that filtering water can provide numerous benefits, from removing toxins and pathogens to reducing hardness and improving its smell and taste.
But is filtered water really healthier for you than tap water?
A wide selection
Those who prefer to filter their own water can choose from a variety of systems for the process.
Jug-like filters, which are placed on the faucet itself, tabletop or refrigerator purifiers and those under the sink, to name a few.
The simplest ones cost only a few dollars, while more complex devices (think devices that work on Wi-Fi, monitor water use and detect plumbing problems) can be four figures.
Water filters fall into two main groups, says Kyle Postmas, who oversees filter certification at the National Sanitation Foundation (NSF), an independent certification organization in Michigan, USA.
"Point-of-use filters filter the water just before it enters the glass, while point-of-entry filters treat the water as soon as it enters the home or building," says Postmas.
Filters also differ in the type of material they are made of and use various technologies.
Absorption, ion exchange, reverse osmosis and mechanical separation are among the more popular ones that separate water from other molecules.
"Different filters can serve different treatment goals," says Detlef Knapp, professor of civil engineering at North Carolina State University.
"There are many different layers," he adds.
The bottom line is to find out what's in your water and whether it needs treatment, and then find the right filters for it.
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The last line of defense
Of course, the potential benefit of filtering your tap water depends on where you live.
In developing countries, where communities have trouble accessing clean drinking water, "the primary problem we worry about is usually bacteria like Escherichia coli and legionella," says Brent Krieger, professor of chemistry and co-director of the Institute for World Water Research at the College of Michigan. Hope.
Contaminated water can cause diarrhea, a preventable disease that kills an estimated million people per year, almost half of them are children under the age of five.
Water filters, however, "can be very effective at stopping bacteria," says Krieger, whose team has led similar initiatives in Latin America.
In one such trial, they installed filters in homes in 16 villages in the Dominican Republic.
This led to decrease in the incidence of diarrhea from 25,6 percent to less than ten percent, which had other positive sides, as a consequence of the domino effect.
"Children miss school less and adults miss work less, which also brings financial benefits to families," Krieger says.
In the Western world, drinking water is strictly regulated and generally considered safe.
The US, for example, they have a law which requires water suppliers to meet certain water quality standards and processing more than 90 toxins which could be found in public drinking water.
In the UK, water goes through multiple rounds of filtration followed by ultraviolet disinfection and chlorination before it reaches users' taps.
This country shares first place by the quality of drinking water and sanitation at Environmental performance index Yale University's 2022 Biennial Assessment of Global Sustainability, with Finland, Iceland, Norway, Switzerland and the Netherlands.
"In most of these Western countries, the water supplier has to do regular testing and inform the public about it," says Krieger.
"Just because you have a massive municipal water system doesn't mean everything is definitely fine," he adds.
Regulation must dictate the amount of lead allowed in pipes, but this does not always apply to those in residential properties, which can be problematic, especially in older houses.
"Rusty pipes are a big problem. I see a lot of toxic lead from old water pipes," says Nirusa Kumaran, a London-based doctor and medical director of the HUM2N wellness center.
In these cases, filters can be useful to remove lead from the water.
In addition, Kumaran says they can also represent the last line of defense against other toxins and chemicals present.
"We see residues of certain drugs - hormone therapy, contraceptive pills, certain psychoactive drugs - that are still in our water system.
"They come from your urine, so when you pee out your medication, it ends up in the rivers," she explains.
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Stopping permanent chemicals
One toxin in tap water that worries some experts is the group of more than 15.000 artificial chemicals by name PFAS, which stands for per- and polyfluoroalkyl substances.
Also called "persistent chemicals" because they remain in the environment without breaking down, PFASs are related with a multitude of health problems, between them cancer, liver disease i reduced fertility.
"We worry about even very low levels of chemicals because some PFASs can bioaccumulate in the human body in a pretty dramatic way.
“There is a low level of PFAS at the moment in almost all water supplies around the planet", says Knapp.
For example, at least one PFAS has been detected in drinking water samples taken from 17 out of 18 UK water companies in 2023.
In the US, PFAS is present in 45 percent of tap water, and six out of every 10 people are believed to be exposed to these chemicals.
Fortunately, filters can help remove these harmful chemicals.
In a study published in 2020, Knap and his fellow researchers found that reverse osmosis and two-stage filters installed under the sink (with mechanical and activated carbon filters) were able to remove almost all of the PFASs they found.
Postmas, whose organization accredits a wide range of products, including water filters, recommends three types of water filters: activated carbon, ion exchange and reverse osmosis.
"We've been certifying filters to reduce PFAS for almost six years now, and we have data to show that they're effective," he says.
Warning to consumers
Although filters can be useful in removing harmful chemicals from our water, they sometimes useful minerals are also removed.
These include magnesium and calcium, as well as iron and manganese, which are removed to make the water softer in one case, and to prevent discoloration in the other.
Filters can also remove fluoride, which some municipalities add to tap water in the fight against tooth decay.
Moreover, reverse osmosis filters, which Knapp says are some of the most effective barriers, "because they manage to get everything out," are sometimes sold with remineralization cartridges that try to add beneficial minerals back into the filtered water.
Some people add a pinch of salt to their own filtered water, but there is currently no evidence that this is effective in restoring lost minerals.
But frankly, it's much more important to get these key compounds from your diet, says Kumaran.
"We should not rely on our drinking water as the main source of minerals," he adds.
Another disadvantage of water filters is that they can sometimes cause more harm than good, especially if the cartridges are not changed regularly.
Sponge-like activated carbon filters can serve as breeding grounds for nasty bacteria.
In a small study conducted in Singapore comparing "tap water" with filtered water samples from the same household, most tap water samples contained around 500 bacteria, within local safe limits.
By comparison, that figure was between 9.000 and 25.400 bacteria for 60 percent of the filtered water samples, with the highest result coming from a filter that was a month past its replacement deadline.
In another study, water left to sit in a siphon or filter under the sink, even just overnight, was found to have an increased concentration of bacteria.
In order to avoid this, it is advised to let the water run through your water filter for at least ten seconds before drinking from it.
"At the very least, if you don't maintain your filter properly, you won't get any more use out of it.
"Or, in the worst case, you can have much worse water coming out of it than what's going into it," Knapp says.
Hydration above all else
When all is said and done, deciding whether or not to use a water filter comes down to being aware of what type of water you have in your area, as well as your comfort and acceptance level of what's in the water.
"If you do just a little bit of homework, you can often find information about what the quality of your drinking water is," Krieger says, explaining that water companies are usually required to publicly and freely release test results.
Plus, "you can hire companies to test your water if you're concerned about it," he says.
If you think your tap water doesn't meet certain criteria, the next step is to find an appropriate filter that fits your home and lifestyle, and can remove the toxins present.
It's hard to recommend one specific type or species, Postmas says, but it's crucial that whatever you end up choosing is certified.
"If the device is certified, then at least you know it's effective," he says.
For Kumaran, staying hydrated is far more important than whether or not someone drinks filtered water.
"As a general practitioner, I encounter many problems as a result of dehydration," he adds.
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