What Is Hard Water?

PICKI NIKI14 de junio de 2026 2 min read

In short

Hard water simply means more dissolved calcium and magnesium. It is safe to drink, not dirty or contaminated.
Hardness is measured in mg/L calcium carbonate, and cities vary widely: Seoul is soft (~61), Berlin is very hard (~303).
Hard water mainly affects how your skin, hair and soap feel, not your health.
A shower filter is not a water softener. It targets chlorine, particles and pH rather than removing minerals.

Hard water is one of the most common water-quality terms people encounter after moving to a new city, and also one of the most misunderstood. Most people don't think about their water until something changes: you move somewhere new, your hair starts feeling different, or white marks appear on the shower glass and never quite disappear. That's usually the moment a term you'd never paid much attention to suddenly matters – hard water.

Hard Water Is Not Dirty Water

One of the biggest misconceptions is that hard water means poor-quality water. It doesn't. Hard water simply contains higher levels of naturally occurring minerals – primarily calcium and magnesium – that the water picks up as it moves through rock and soil. In many parts of Europe this is completely normal, and some of the cleanest drinking-water systems in the world are also hard-water systems. Hard water isn't contamination. It's chemistry.

What Makes Water Hard?

As water moves through the ground, it dissolves minerals from rock and soil. The more calcium and magnesium it picks up, the harder the water becomes. Hardness is commonly measured as milligrams per litre of calcium carbonate equivalent (mg/L CaCO₃). A simplified guide:

Classification	Hardness
Soft	below 75 mg/L
Moderately hard	75–150 mg/L
Hard	150–300 mg/L
Very hard	above 300 mg/L

Commonly used hardness classifications based on calcium carbonate (CaCO₃) concentration. Reference: World Health Organization, Hardness in Drinking-water (2011).

Not All Water Is the Same

The difference between cities can be substantial.

~61

Seoul

mg/L CaCO₃ — soft water.

Soft

~250

Paris

mg/L CaCO₃ — hard.

Hard

250-300

London

mg/L CaCO₃ — hard.

Hard

~303

Berlin

mg/L CaCO₃ (17°dH) — very hard.

Very hard

Sources: Seoul Arisu Waterworks; Eau de Paris / ARS Île-de-France; Thames Water; Berliner Wasserbetriebe.

For someone moving from Seoul to Berlin, the water contains around five times more hardness minerals. It isn't just something you measure – for many people, it's something they notice in their hair, skin and shower environment.

What Hard Water Can Affect

Hard water doesn't affect everyone the same way. Some people notice very little; others notice changes almost immediately. Common experiences include:

Hair that feels rougher or harder to manage
Increased mineral residue on skin and hair
Soap that feels harder to rinse away
Limescale around taps and shower heads
Skin that feels less comfortable after showering

These experiences vary from person to person, and water hardness is one of several variables involved.

Hard Water Is Not the Enemy

At PICKI NIKI, we don't believe every mineral needs to be removed. Hard-water minerals aren't inherently bad: calcium and magnesium occur naturally throughout the environment and are safe to drink. The challenge isn't that the water is unsafe – it's how that water interacts with skin, hair and the shower environment over repeated exposure. That's an important distinction.

Why We Don't Try To Remove Every Mineral

PICKI NIKI is not a water softener. Hard water remains hard. Instead, we focus on the variables a shower filter can realistically influence: neutralising chlorine, capturing particles, and bringing alkaline water toward a more skin-friendly pH. The vitamin C stage also interacts with hard-water minerals through a mild chelating action – not strongly enough to soften the water, but it may help reduce the residue they leave behind on skin and hair. You can read more about how that works on the Why It Works page.

Our goal was never to remove every mineral. It was to create water that works better for skin and hair, with the water people already have.

Evidence & sources

References

Sources supporting the claims in this article. Peer-reviewed papers are cited for the underlying mechanisms, not as proof of product efficacy.

UK Drinking Water Inspectorate Water Hardness - Consumer Guidance, 2024

Hard water is caused by dissolved calcium and magnesium; it is safe to drink.

Thames Water Water hardness data, London / Thames Valley, 2026

Regional hardness figures for London and the Thames Valley.

Danby SG et al. Journal of Investigative Dermatology, 2017

Hard water increases surfactant deposition after washing, linked to skin irritation.

Jabbar-Lopez ZK, Craven J, Logan K, et al. British Journal of Dermatology, 2020

Longitudinal analysis of water hardness and atopic eczema; gene-environment interaction.

About the author

PICKI NIKI

PICKI NIKI builds filtered shower heads designed in Germany and manufactured in Korea - with third-party testing and honest, checkable claims.

Frequently Asked Questions

Is hard water safe to drink?

Yes. Hard water is safe to drink and does not pose a health risk. The minerals it contains — primarily calcium and magnesium — are naturally occurring and consumed in food and water worldwide. The question hard water raises is not safety, but how it interacts with skin, hair and household surfaces.

How do I know if my water is hard?

The most common signs are white limescale deposits around taps and shower heads, soap that feels difficult to rinse away, and spots on glassware after washing. If you've recently moved from a soft-water city such as Seoul to a harder-water city such as Berlin, London or Paris and noticed changes in how your hair or skin feels, water hardness is worth investigating. You can check your local water supplier's annual water quality report for a hardness figure in mg/L CaCO₃.

Does hard water cause hair loss?

No. Hair loss has medical and genetic causes. What hard water can do is affect the surface condition of hair — mineral deposits on the hair shaft can make it feel rougher and harder to manage over time. A shower filter is not a medical product and makes no claim to treat or prevent hair loss.

While hard water is not considered a cause of hair loss, some people find that mineral build-up can leave hair feeling rougher, heavier or harder to manage. Reducing those stressors may improve how hair looks and feels, but it should not be confused with treating hair loss.

Does a shower filter soften hard water?

No. True water softening — removing calcium and magnesium ions — requires an ion-exchange system, not a compact shower filter. A shower filter addresses different variables: neutralising chlorine, capturing particles, and in the case of a vitamin C filter, bringing alkaline water toward a more skin-friendly pH. Hard water remains hard after passing through a shower filter. That's why we describe PICKI NIKI as a shower filter, not a water softener.

What is the difference between hard water and soft water?

Soft water contains low concentrations of dissolved minerals — typically below 75 mg/L CaCO₃. Hard water contains significantly more, often 150–300 mg/L or above. The difference affects how water feels on skin and hair, how soap lathers, and how quickly limescale builds up on surfaces and appliances.

Is hard water bad for skin?

Not necessarily. Hard water is safe and widely consumed around the world. However, some people report that hard water feels less comfortable on their skin, particularly when combined with chlorine and repeated daily exposure. Individual experiences vary, which is why water quality is best thought of as one variable among many rather than the sole cause of a skin concern.