ZeroWater Knowledge Center

Limescale in Tap Water

Everyone can agree that limescale is a nuisance. It accumulates on taps and showers, in kettles and coffee-machines, making them hard to clean. But what effect does it have on health? In this article we’ll explore where limescale comes from, whether it is bad for your health, what you can do to protect your appliances, and how to remove it from your tap water.

What is limescale?

Limescale is the white, chalky deposit that builds up inside your kettle, shower, water pipes or anywhere hard water has flowed. It is made up of minerals, mainly calcium and magnesium carbonate.

Water that contains a lot of dissolved minerals (or limescale), is called hard water.

In Europe, the hardness of the water is indicated in degrees of General Hardness (dGH), also known as deutsche Härte or  ‘German Degree’ (dH). One dH equals 17,9 milligrams of calcium carbonate per litre (mg/L).

Classification for hard and soft water:

  • 0-4 dH: very soft water
  • 4-8 dH: soft water
  • 8-12 dH: average water
  • 12-18 dH: fairly hard water
  • 18-30 dH: hard water

Hard water, soft water, and water pH

The pH of the water refers to how alkaline or acidic the water is. Water that has moderate hardness (8 to 18 dH), tends to be neutral (pH 7) or slightly alkaline (pH 7.1-9). That’s because the minerals in the water neutralise any acidic substances.

How does limescale end up in your tap water?

The longer water is in contact with minerals, the harder it becomes; for example ground water that flows through limestone or marl absorbs some of the minerals in the rock.

Tap water in Europe is extracted from surface water (lakes, rivers, streams) and groundwater (natural underground water reservoirs). In both cases, the water has been in contact with limestone or other rocks, and therefore contains dissolved minerals.

Water companies put drinking water through a series of processes to clean and purify it, but do not remove all the minerals. As a result, the water that flows from your tap usually contains minerals that cause limescale.

What are the potential health impacts of limescale?

In and of itself, hard water is not damaging to health. After all, the minerals it contains – especially calcium – are important for health.

Calcium is essential for strong bones, muscles and teeth. The recommended daily intake of calcium for adults between 19-50 years old is 1000 mg/day. The tolerable upper intake is 2500 mg per day.

Balance is key – whether for the health of your body, or that of your appliances. It is important not to have too much calcium, because this can interfere with the body’s absorption of other essential nutrients such as zinc and iron. Too much calcium can also increase the risk of kidney stones and weak bones.

For reference, one litre of averagely-hard water (8-12 dH) contains between 143,2-214,8 mg of calcium carbonate – well below the recommended daily intake.

What about soft water?

According to the WHO, soft drinking water – just like hard water – has no effect on health.

Softer water can be better for people with sensitive skin (or eczema), but it can also lead to skin irritation because soap does not rinse off properly.

Soft water may not be that good for water installations. In fact, concrete (sometimes used for water distribution pipes) can dissolve in soft water. In this case, hard water is better because the minerals it contains deposit on the inside of the water pipes, protecting them and helping them last longer.


According to the World Health Organisation’s Guidelines for Drinking Water Quality, water with a hardness of 200 mg/L calcium carbonate (around 11.2 dH) causes limescale deposits on water pipes. Water with a hardness of less than 100 mg/L (around 5.62 dH) may be more corrosive to water pipes.

However, the guidelines do not recommend any minimum or maximum calcium or magnesium concentrations in drinking water. They propose no guideline values because while there is some evidence of a protective effect of hard water on cardiovascular health, the evidence is not solid and the intake of these minerals depends on many other factors, such as diet.

The European Union’s latest Drinking Water Directive does not specifically set limits for calcium or magnesium. Instead, it notes a general obligation for member states to set their own recommendations or limit values.

The Directive states:

“Water should not be aggressive or corrosive. This applies particularly to water undergoing treatment (demineralization, softening, membrane treatment, reverse osmosis, etc.).

Where water intended for human consumption is derived from treatment that significantly demineralizes or softens water, calcium and magnesium salts could be added to condition the water in order to reduce any possible negative health impact, as well as to reduce the corrosiveness or aggressivity of water and to improve taste. Minimum concentrations of calcium and magnesium or total dissolved solids in softened or demineralized water could be established taking into account the characteristics of water that enters those processes.”

The following table shows the regulations, recommendations or guidelines taken by different European countries.

CountryType of regulationLimits
AustriaGuidelinesMaximum calcium 440 mg/L Maximum magnesium 165 mg/LMinimum water hardness 8.4 dH
BelgiumLegislative ActMaximum Calcium 270 mg/LMaximum magnesium 50 mg/LMinimum water hardness 8.4 dH
BulgariaLegislative ActMaximum calcium 150 mg/LMaximum magnesium 80 mg/LMaximum water hardness 33.6 dH
CroatiaLegislative ActCalcium, magnesium and water hardness are listed as parameters but without a set limit. Just a note “The recommendations of the WHO are used to interpret the results obtained.”
CyprusGuidelinesNo legislative standard for water hardness. Contracts for operating desalination plants state water hardness should range between 4.48-8.4 dH with minimum 30 mg/L of calcium.
Czech RepublicLegislative ActCalcium content between 40-80 mg/LMagnesium content between 20-30 mg/LWater hardness between 11.2-19.6 dH 
DenmarkNo recommendation or legislation
EstoniaNo recommendation or legislation
FranceNo recommendation or legislationRecommendation only specifies that drinking water must not be corrosive or aggressive, and has to have calcium-carbonate balance. 
GermanyGuidelinesDrinking water hardness equal or above 14 dHHot water hardness equal or above 8.4 dH
GreeceNo recommendation or legislation
HungaryRecommendationWater hardness between 5.04-35 dH
IrelandNo recommendation or legislation Education of public / water producersThe website of water company Irish Water states hard water is not softened because hard water may offer more benefits due to higher mineral content.
ItalyRecommendationWater hardness between 8.4-28 dH
LatviaNo recommendation or legislation
LithuaniaNo recommendation or legislation
LuxembourgNo recommendation or legislationEducation of public / water producersThe website of Luxembourg’s water management department states that the water must retain residual hardness of 6-9 dH.
MaltaNo recommendation or legislation
The NetherlandsRecommendationWater hardness above 5.6 dH
PolandRecommendationWater hardness between 3.36-28 dHMagnesium 7-125 mg/L (as long as sulphate content is less than 250 mg/L)
PortugalRecommendationMaximum calcium 100 mg/LMaximum magnesium 50 mg/LWater hardness between 8.4-28 dH
RomaniaRecommendationMinimum water hardness 5 dHNo upper limit
SlovakiaRecommendationWater hardness between 6.16-28 dH
SpainGuidelinesNo minimum level of water hardnessWater pH between 6.5-9.5
SwedenGuidelines Calcium between 20-60 mg/L
United Kingdom (England and Wales)GuidelinesIt is recommended that water companies maintain a minimum hardness of 8.4 dH. 
United Kingdom (Scotland)Education of public / water producersDrinking Water Inspectorate website states that “it remains prudent not to undertake softening of drinking water supplies … it appears sensible to avoid regular consumption of softened water where there is an alternative”. 

Limescale in tap water in The Netherlands

The Dutch Drinking Water Decree states that water hardness should be above 5.6 dH, but does not offer a maximum limit.

Since there are many different drinking water sources, the water’s degree of hardness is almost never the same. According to Waternet, the average hardness of water in the Netherlands is 8 dH.

The areas in the Netherlands with the hardest water are: Stadskanaal, Vlagtwedde, Bellingwedde, Hoogezand-sappemeer, Slochteren, Veendam, Menterwolde, Pekela, Oldambt, Winsum, Bedum, Ten Boer, Loppersum, De Marne, Appingedam, Delfzijl and Eemsmond.

Limescale in tap water in France

Water regulation in France does not specify a limit for water hardness. It only states that water should be of a pH between 6.5 and 9, and have a calcium-carbonate balance that ensures the water is neither too aggressive (or too soft) nor too scaling (too hard).

Since water is extracted from many different sources, the degree of hardness is never the same. In France, the following regions have the hardest water: 

  • Nord-Pas-de-Calais – millions of years ago, this area was under the sea and had a tropical climate. This made the soil very chalky, hence why this is one of the regions with the hardest water.
  • The Alps – the Alps are made up of sedimentary rocks, and therefore very chalky. elles sont composées de roches sédimentaires et donc très calcaires.
  • Jura – has soils made up of 95% lime.
  • IÎle-de-France – where soils are very chalky, and therefore full of lime. 

To know how hard your water is, you can check this interactive map: 

Limescale in tap water in Italy

Legislation in Italy recommends that water hardness be between 8.4-28 dH.

According to a study by the water softening company Culligan, 883 municipalities in Italy have hard water. The cities with the hardest water (above 16.8 dH) are Rome and Bologna. Cities with moderately hard water (8.4-16.8 dH) were Milan, Turin, Bari and Florence.

Limescale in tap water in the UK

The UK’s drinking water quality regulations do not specify standards or limits for water hardness, calcium or magnesium. The Drinking Water Inspectorate (DWI), part of the Department for Environment, Food and Rural Affairs (DEFRA), makes a recommendation that when water companies artificially soften the water, they must maintain a minimum hardness of 150 mg/L CaCO3 (equivalent to 8.4 dH).

According to the DWI, the regions with the hardest water (above 16.9 dH) are the East of England, East Midlands, and Yorkshire. The regions with the softest water (lower than 5.6 dH) are the South East, and Wales.

Limescale in tap water in Ireland

Ireland’s drinking water regulations do not set limits for water hardness.Water company Irish Water’s website states that hard water is not harmful to health, and that the higher mineral content may even provide health benefits. It also states that it does not soften water because “there is no legislative requirement to remove hardness from drinking water” and hard water typically tastes nicer.

Regions in the centre of Ireland tend to have the hardest water (between 17-22 dH), while Kerry, Cork, Waterford, Wexlow, Wicklow and Dublin have a water hardness of between 11-17 dH.

You can input your address into Irish Water’s website to find out the water hardness in your area. Click here: 

Limescale in tap water in Germany

The German Drinking Water Ordinance only provides guidance relating to water hardness. It recommends that tap water should be equal or above 14 dH, and hot water should be equal or above 8.4 dH. It does not provide a maximum limit value for water hardness.

Limescale in tap water in Spain

The drinking water regulation in Spain does not state a maximum limit for water hardness, calcium or magnesium content. All it does is stipulate that tap water’s pH should be between 6.5-9.5.

Limescale in tap water in Poland

In Poland, the Minister of Health’s regulation on water intended for human consumption makes the following recommendations:

  • Water hardness should be between 3.36-28 dH
  • Magnesium content should be between 7-125 mg/L

However, the regulations also state that these recommended values are made for health reasons, and do not impose an obligation for water companies to adhere to them.

Limescale in tap water in the USA

The Environmental Protection Agency has not set a legal limit for hardness in water. That is because it considers that the primary minerals involved in hardness – calcium and magnesium – are not toxic to health.

The states with the hardest water are Montana, Wyoming, Utah, Colorado, Arizona, Texas, Oklahoma, Kansas, Nebraska, South Dekota, Illinois, Indiana, Pennsylvania, and West Virginia.

You can take a look at the United States Geological Survey map of water hardness for more details: 

What can you do to remove limescale from water?

So it seems that the issue with hard water and limescale is not their effect on health, but how they affect appliances.

Limescale is, let’s face it, a household annoyance. The problem arose from the middle of the last century, when we began using more appliances. Limescale forms because calcium reacts with carbonate when water is heated. Boilers, washing machines, dishwashers, kettles and coffee machines can therefore become prone to “scaling”.

How to keep your kettle and coffee-machine free from limescale

Limescale usually builds up on heating elements, resulting in appliances being less efficient and more energy-hungry. This is then reflected in your energy bill. The softer the water, the less limescale build-up, and the better your appliances can run. If you fill your kettle or coffee machine with filtered water, you avoid the limescale build-up and protect your appliances.

Several filters can remove the minerals from your drinking water, such as reverse osmosis or the ZeroWater filter.

ZeroWater eliminates limescale from your tap water

Do you want to protect your household appliances against limescale and remove limescale from your drinking water? ZeroWater removes 100 percent limescale from water. Our filter also removes lead, glyphosate, chlorine, PFAS (PFOS/PFOA) and more. Take a look at our online shop and start protecting your kettle and coffee machine today.