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Tap, filter, bottle or sparkling water

Headlines that fizzy water can help you lose weight are misleading – and other health claims around bottled and filtered water also should be taken with a pinch of salt

This is Everyday Science with Clare Wilson, a subscriber-only newsletter from The i Paper. If you’d like to get this direct to your inbox, every single week, you can sign up here.

Hello, and welcome back to Everyday Science.

This week I have been digging into claims that sparkling water can help you lose weight, and it made me look closer at the range of health claims around various kinds of bottled and filtered water.

Judging by the growing numbers of us carrying around personal water bottles, as well as the rows of bottled water on supermarket shelves, the health messages about the importance of being well hydrated seem to have sunk in.

Despite warnings over its carbon footprint, people in the UK are buying more bottled water than ever, whether still or sparkling. Sales are predicted to continue growing by about 5 per cent a year, according to market research firm Grand View Research.

Use of home water filters – either in the form of jugs kept in the fridge, or more sophisticated systems linked to the plumbing – is forecast to rise even faster, by 11 per cent a year across Europe.

People may cite several reasons for turning away from tap water, including its taste, worries over contaminants and its levels of dissolved minerals, also called the water “hardness”. So, which of these concerns stack up?

Dr Francis Hassard, a microbiologist at the Cranfield Water Science Institute, said the bad public image of our drinking water quality is undeserved.

The poor perception may stem partly from incidents when water companies have released sewage into rivers and the sea, which there has been growing awareness of because of closer monitoring of such discharges. “There’s a fair amount of negative perception associated with the UK water industry,” said Dr Hassard.

Distrust in tap water may also be driven by misleading advertising from water filter firms, according to the Drinking Water Inspectorate (DWI), a government body that checks tap water quality in England and Wales.

Filter manufacturers often claim that tap water needs treatment in the home to remove substances such as pesticides, particulate matter and nitrates.

Quality checks

In fact, water companies use multiple systems for filtering, cleaning and disinfecting water before it reaches our homes. “Tap water is safe to drink and there is no need to install additional treatment within the home as a health protection measure,” says the DWI.

Drinking water has to have numerous quality checks. “UK water companies routinely test for at least 50 to 60 core parameters, as required by law, and often monitor additional substances, leading to tests for hundreds of potential contaminants in total,” said Dr Hassard. These include a long list of different species of bacteria, minerals, organic chemicals (including pesticides), as well as properties such as odour and clarity.

Occasionally, if tests reveal that contaminants have got into the drinking water supply, water firms will issue “boil notices” to the public, telling them to boil tap water before drinking it. This happened last year in Brixham, in Devon, when a parasite from cow manure got into a pipe that passed through a field. But incidents like this are relatively rare, said Dr Hassard. “We have fewer boil notices than equivalent European countries.”

UK tap water usually ranks in the top 10 in terms of quality out of a long list of other countries, as measured by the Environmental Performance Index, an international rating by Yale and Columbia Universities.

The strict rules around tap water mean it is subject to more monitoring than some bottled water. “People think their bottle of water is of better quality,” said Dr Hassard. “Actually, the opposite is true.

“Bottled water is still a very good quality product,” he added.

But this can vary by country, as different places have different testing regimes for tap and bottled water. If buying bottled water abroad, the NHS advises people to use products from well known manufacturers and to check the seal is intact.

It is also possible for tiny particles of plastic, known as microplastics to leach into bottled water, he said. Microplastics have been tentatively linked to heart disease and various other conditions, although the research is at an early stage.

“The levels of microplastics in UK tap water is very, very low, often below detection. But in bottled water, you can often find them,” said Dr Hassard.

Fizzy water

Safety aside, some people buy bottled water because of perceived health benefits. Sadly, the headlines this week claiming that sparkling water can help you lose weight should not be trusted.

They were based on a paper where a Japanese doctor discussed if the carbon dioxide in sparkling water might make your blood more acidic, which could cause your metabolism to use up glucose.

A press release was issued, with the misleading headline saying “fizzy water might aid weight loss by boosting glucose uptake and metabolism”, although the text then acknowledged that the effect would be so small, it couldn’t be “relied on” to shed pounds.

In fact, the analysis did not calculate how much glucose would be used up by a drink of sparkling water. The paper stated, however, that, for comparison, even a four-hour session of haemodialysis, which also makes blood more acidic, uses up just 10 grams of glucose. A fizzy drink would make blood more acidic for only a few minutes – suggesting it would use up negligible glucose, the author, Dr Akira Takahashi at Tesseikai Neurosurgery Hospital in Shijonawate, told me. “Glucose consumption from carbonated water cannot be expected,” he said.

Fizzy drinks might help in weight loss because they make people feel fuller – although previous studies testing this theory have given inconsistent results.

How about bottled water with added ingredients that are supposed to give extra benefits? Electrolyte water, with added minerals such as sodium and calcium, is often targeted at people doing exercise, to replace those compounds lost in sweat.

While such drinks may be helpful for professional athletes or people running marathons, for most, they are pointless because we get all the minerals needed from food, said Dr Nidia Rodriguez-Sanchez, a physiologist at the University of Stirling.

There is similarly no benefit to drinking water with added vitamins. “The amount of vitamins provided is minimal,” she said. “If we’re not eating vegetables, having vitamin water won’t make a difference.”

Question of taste

Nevertheless, some people prefer to drink bottled or filtered water because they feel it tastes better than tap water. One reason may be that some people can detect residual levels of chlorine in tap water, which is added to kill bacteria and other possible germs.

Chlorine can be removed by the most common kind of home filter system, where the water must pass through tiny holes in a layer of carbon inside replaceable cartridges. This should also help to remove any remaining bacteria or organic compounds.

But it is essential that filters are cleaned and maintained, with the cartridges replaced as often as advised. “Failure to do so will cause a build-up of deposits and create a breeding ground for bacteria,” said the DWI.

In homes where filters are connected to the plumbing, it is also worth running the tap for about 10 seconds every morning to flush out any bacteria that may have accumulated inside the cartridge overnight, said Dr Thanh Nguyen, an environmental engineer at the University of Illinois Urbana-Champaign.

Her team recently showed that in a preschool with filters installed in the sinks, bacteria levels were higher in the first water emerging from the taps every morning. “The filter is designed to retain bacteria,” she said. “You can actually concentrate them.”

Hard water

One thing carbon filters will not affect is the water hardness – which refers to the amount of dissolved minerals, mainly calcium and magnesium – and can be another reason people dislike the taste of their tap water. Some might describe it as chalky or metallic tasting.

The hardness varies depending on where you live because rainwater picks up minerals as it soaks through the ground. The south and east of England has harder water, as its chalk and limestone rocks are more soluble.

People are more likely to dislike the taste of their tap water if they live somewhere different to where they grew up, says the DWI.

Another annoyance in hard water regions is that the minerals are deposited as limescale on appliances such as kettles and shower heads. Some people also feel that hard water makes their hair and skin feel less soft.

People may therefore get water softener systems installed into their plumbing, which exchange calcium and magnesium for sodium, although these don’t bring other the benefits of water filtering.

But the higher sodium levels in softened water mean it should not be used for drinking or food for babies or people on low-salt diets as sodium is the harmful constituent of salt. So, if homes have a water softener system to reduce limescale, they are supposed to keep at least one tap delivering regular water in their kitchen.

A further type of water filter, which works through a process called reverse osmosis, removes all minerals and so effectively softens hard water, without adding in sodium. But these systems usually work so well they need to add a small amount of salt back into the water. “If you don’t have any salt, the water tastes really weird,” said Dr Nguyen.

The DWI warns that anyone thinking of getting a water filter system connected to their taps should use a qualified plumber – not door-to-door salesperson, who may offer to test your water for contaminants and provide fake readings, said the DWI. “Scams of this type are not uncommon,” the body said.

The DWI also advises that people first try just keeping a jug of ordinary tap water in their fridge, to see if that improves the taste. Studies suggest that most people cannot tell the difference between tap water and bottled water if both are chilled to the same temperature.

I’ve been watching

I was on the edge of my seat watching the Ralph Fiennes film, Conclave, about the election of a new pope. The script, the acting, the cinematography are all superb, and I would never have guessed the intracies of papal politics would be so fascinating – and machiavellian.

This is Everyday Science with Clare Wilson, a subscriber-only newsletter from The i Paper. If you’d like to get this direct to your inbox, every single week, you can sign up here.



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