Why your tap water could be putting you at risk of dementia: Everything you need to know about the dangers – and the reason medical experts say you SHOULDN’T switch to bottles

Why do people in some parts of the country seem to be more at risk of certain diseases than others?

There are obvious factors, such as smoking rates, income or diet. But now research is pointing the finger of blame at something most of us don’t give a second thought to – the local tap water.

Where you live – and specifically, the ground beneath your feet – affects the levels of minerals such as magnesium, calcium, sodium, iron, potassium and zinc in your water. This doesn’t only determine if water is ‘hard’ or ‘soft’: research has linked it to certain health problems, from bone fractures and eczema to stroke, even cancer.

A study, published this month in the journal Ecotoxicology and Environmental Safety, examined the risk of developing dementia. Researchers sifted through data from almost 400,000 people in the UK and found that those living in soft water areas – which have lower concentrations of natural minerals – had a raised risk of Alzheimer’s disease. One theory is that the minerals may protect the brain.

The authors said their results had implications for public health, suggesting governments might consider tougher regulation to control water hardness in drinking water.

However Dr Emma Anderson, an associate professor of epidemiology at University College London, who researches environmental risk factors for Alzheimer’s disease, questioned the study’s methodology.

Another expert has commentated that any effect from tap water would be ‘very small’ – and there is ‘a bigger risk of dementia from other risk factors such as smoking, high cholesterol and high blood pressure’.

Yet this isn’t the only disease to be linked to hard or soft tap water. So how worried should you really be and are there steps we should take to protect ourselves?

What makes water ‘soft’ or ‘hard’?

‘Water hardness is effectively the concentration of calcium and magnesium in water,’ says Paul Hunter, a professor in medicine at the University of East Anglia, who is an expert in waterborne diseases.

When rain hits the ground it quickly absorbs minerals from the local stone and soil. ‘The most common sources of hardness are limestone (which introduces calcium into the water) and dolomite (which introduces magnesium).

The South Downs in West Sussex for example, which are rolling chalky hills of calcium carbonate, has some of the hardest drinking water in the country, explains Professor Hunter.

Soft water has lower concentrations of minerals because it is typically sourced from rivers and lakes – as is the case in Cumbria and parts of Yorkshire.

‘Hard water also contains iron, manganese, sodium, potassium and zinc,’ adds Professor Hunter.

However, these aren’t factored into calculating the level of hardness, which is usually measured by referring to the quantity of calcium carbonate specifically, in milligrams per litre of water.

‘If there is less than 100mg per litre it is classed as “soft”, anything over that is “hard”, and more than 300 per litre is very hard,’ says Professor Hunter. (The new Alzheimer’s study was based on hard water, defined as containing more than 120mg per litre.)

How can I tell if my water is hard or soft?

If you get little lather from soap, shampoo or washing powders; tide marks on your basins and loo; and limescale in your kettle, chances are you have hard water.

With its high mineral content, hard water can appear cloudy straight out of the tap.

Another telltale sign is ‘scum on the surface of hot drinks, especially tea brewed in the cup with a tea bag’, according to the Drinking Water Inspectorate.

A 2021 study in the journal Physics of Fluids found compounds in tea bond with calcium carbonate in tap water, making a harmless waxy layer on the drink’s surface. It can also affect the tea’s aroma. Soft water tends to taste sweeter; hard may taste chalky, even bitter.

Can hard water protect you?

The new study suggests hard water might offer some protection – for the brain at least. (‘We can’t say from this study whether removing hardness at the tap would increase your risk of Alzheimer’s but that is certainly a concern,’ says Professor Hunter.)

In fact, this seems to resonate with previous research that has suggested hard water is protective of the heart – because it contains high levels of magnesium. This helps the heart maintain a healthy rhythm and is involved in the regulation of blood pressure and cholesterol production.

There is ‘no doubt’ that low magnesium can be a risk factor for cardiovascular disease’, says Professor Hunter.

Indeed, a 2021 study in the journal Nutrients found that people with low levels of magnesium were more likely to suffer a faulty heart rhythm.

Other research has linked hard water to a lower risk of stroke.

A 2022 study in the American Journal of Clinical Nutrition, which looked at more than 36,000 post-menopausal women in Sweden, found that water hardness – especially higher magnesium concentration – was associated with a reduced risk of the condition.

‘But the evidence that drinking hard water with higher magnesium may prevent heart disease and stroke is mixed – the debate is ongoing,’ says Professor Hunter.

‘My view is that association between the minerals in hard water and any health benefits is probably real, but the effect is only seen in populations that otherwise have a low dietary intake of magnesium.’

It may be good for your bones

Research by Dr Cecilie Dahl, an associate professor of epidemiology at the University of Oslo in Norway, suggests higher levels of minerals in hard water, particularly magnesium, may be associated with a reduced risk of bone fractures.

She told Good Health that her research, published in the journal Bone, has shown that men and women with ‘the highest third of magnesium concentrations in drinking water had a reduced relative risk of hip fractures, compared to those in the lowest third.

‘Magnesium appears to play a significant role in these protective effects,’ she says.

‘Drinking hard water could help you reach peak bone mass when you are young, which may impact your fracture risk later in life when you start losing bone.

‘While the contribution of magnesium from drinking water to overall dietary intake is small – approximately 0.2 per cent for men and 0.3 per cent for women in our study – its bioavailability [i.e. how well our bodies can absorb it] in water is typically higher compared to food sources.’

(Indeed magnesium in water may be better absorbed than from supplements – which may result in just 4 per cent actually being absorbed into the body, according to a 2002 study in the American Journal of Clinical Nutrition.)

‘This may explain why even small amounts of magnesium in water can have measurable health benefits,’ says Dr Dahl.

Her advice for people in soft water areas is that having ‘an adequate magnesium and calcium intake through diet or supplements is essential for bone health.

‘Foods rich in magnesium, such as nuts, seeds, wholegrains and leafy green vegetables, are excellent options. Calcium can be obtained from dairy products and fortified foods – or supplements if dietary intake is insufficient.’

Could water type affect cancer risk?

A number of studies have shown possible links between drinking hard water and reduced risk of some cancers.

For example, research has suggested that the calcium and magnesium in drinking water may reduce the risk of gastric cancer.

One theory is that magnesium improves the ability of the immune system to eliminate potentially cancerous cells.

However Professor Karol Sikora, former chief of the World Health Organisation Cancer Programme and a cancer specialist based in London, told Good Health: ‘The results are complicated. There is no universal relationship between cancer incidence and water hardness.

‘For example, bladder cancer cases seem to increase in number in hard water areas, but stomach cancers drop. It may not be the calcium carbonate in water that matters but something else.’

What it means for your hair and skin

Hard water may lead to both dry hair and skin, says Dr Justine Hextall, a consultant dermatologist at the Tarrant Street Clinic in Arundel, West Sussex. ‘When we wash with hard water, the high calcium content reduces the solubility of surfactants (i.e. detergents) in soaps and shampoos.

‘These surfactants therefore tend to stay on the skin, causing dryness and irritation – and can impair barrier function,’ she says. ‘They have a similar effect on hair, leaving it dry and dull.’

In a 2015 study in the International Journal of Dermatology, researchers washed hairs taken from 15 women with hard water, and another set with distilled soft water for ten minutes on alternate days for 30 days.

Placed under a microscope, the hair washed in hard water was less thick and coarser. Some cleansers and shampoos are designed to remove unwanted minerals from hair and skin, says Dr Hextall.

Hard water can be particularly problematic for some people, raising the risk of eczema and other forms of dermatitis (inflamed, irritated skin).

Professor Carsten Flohr, a dermatologist and founding director of the International Eczema Council, led a study ‘which suggested that softening water in those at high risk of developing eczema may be a good way of preventing the disease’.

However, he says this was a pilot study with a small number of babies. ‘A larger, multi-centre study is required to answer the question whether softening water from birth can prevent eczema.’

The likelihood is that the eczema is both a direct result of irritation of the skin by calcium carbonate in domestic water supplies, and the minerals being absorbed into the body, he explains.

Genetics also play a part: ‘Babies living in a hard water area with a mutation in the filaggrin gene [which controls the formation of the skin barrier] have a significantly higher risk of developing eczema,’ he says.

Hard water, which is alkaline, may also change the pH balance of skin (which should be slightly acidic to keep bacteria levels down), leading to acne flare-ups.

Steps to reduce irritation include not washing delicate facial skin in the shower, says Dr Hextall: ‘I recommend washing sensitive facial skin after the shower, for many reasons – [for instance] the heat of shower water can reduce natural oils that help to protect the skin from moisture loss.’

Instead, use a rich cleanser after the shower, then a serum containing compounds like hyaluronic acid and glycerin that trap moisture. Afterwards, apply a facial moisturiser with ingredients such as shea butter that mimic the natural oils and fats in a healthy skin.

‘This combination is ideal for soothing and hydrating an eczema-prone skin on the face and for creating a more robust skin barrier that will be able to withstand external aggressors such as hard water,’ says Dr Hextall.

When it comes to body skin, she adds that ‘in a hard-water area where surfactants will build up, driving dryness and irritation, it is all the more important to encourage a gentle approach’ – gentle cleansers and hydrating skincare.

Water type and kidney stones

Kidney stones form when minerals and salts in urine create hard deposits in the kidney. Calcium stones are most common.

But Professor Christopher Eden, a consultant urologist at London Bridge Hospital, says calcium from drinking water is not a risk for most, as excess calcium is normally harmlessly excreted.

‘Drinking hard water or eating calcium-rich foods such as cheese and nuts only increase the risk of urinary tract stones if you have a rare genetic disposition that causes the kidneys to excrete too much calcium or oxalate, or both.’

• To find out about the water quality (including hard/soft water) in your area, go to your water company’s website and use the postcode checker.

Should you get a water softener or filter jug?

If you live in a hard water area, then a softener can increase the life of domestic appliances because it reduces limescale build-up – but it is not recommended for the water you intend to drink.

According to the Drinking Water Inspectorate: ‘This is because most water softeners work by replacing the hardness [caused by magnesium and calcium] with sodium. Too much sodium can be a problem for premature babies because their kidneys are not good at filtering it out of the blood, and for people on a low sodium [i.e. low salt] diet.’

Too much salt is a risk factor for high blood pressure. However, naturally occurring soft water containing sodium is not thought to raise blood pressure.

Professor Gerry Carr-White, a consultant cardiologist at Guy’s and St Thomas’ NHS Trust in London, says there’s no good evidence that drinking either hard or soft water has any effect on blood pressure.

If you have sensitive skin or want to wash your hair in water with fewer impurities, water filters that fit on your shower head can remove some particles and chlorine, but they are less effective at removing minerals that cause hard water. Dermatologist Dr Justine Hextall says that these systems may be useful for some people who have sensitive skin or eczema.

‘While I don’t believe the concentration of chlorine and other minerals in tap water is enough to cause significant irritation to skin, there is no harm in putting on a shower filter, apart from the cost of replacement filters,’ she says.

As for a filter jug for drinking water, ‘most if not all filters on the market targeted at the general public remove hardness and many other minerals as well as heavy metals including lead’, says Paul Hunter, a professor in medicine at the University of East Anglia. ‘This is one reason I would definitely use a filter.’

So what about bottled water?

Switching to plastic bottles may not be the answer. An average litre bottle of water contains almost a quarter of a million minuscule plastic fragments, found a study last year by Columbia and Rutgers Universities in the US.

The researchers analysed samples of three common bottled water brands and found 110,000 to 400,000 nanoparticles of plastic, and said much of this appears to have come from the bottle itself.

Several studies have shown that nanoplastics were able to cause inflammation and cell death, for instance, according to a 2021 review in the journal Nanomaterials.