Hair

Hard water and hair: London, Copenhagen, Paris, Warsaw

15 September 2026

Water hardness is the dissolved calcium and magnesium load. It is given in milligrams of calcium carbonate per litre (mg CaCO₃/l) or in German degrees (°dH). Conversion: 1 °dH ≈ 17.8 mg CaCO₃/l.

A rough scale: below 100 mg/l — soft. 100–200 — moderately hard. 200–300 — hard. Above 300 — very hard.

Where the water is hard — London, Copenhagen and the rest of the map

Hardness is geology, not “water quality”. Chalk and limestone make hard water. Granite, gneiss and moorland make it soft. Two capitals in the same country can therefore feel completely different in the shower.

United Kingdom. The split is geological. The south-east and east of England sit on chalk and limestone; the north and Scotland sit on granite and moorland.

• —London — Thames Water typically reports 250–400 mg/l, from hard to very hard. The water comes from the chalk of the Thames valley, the Chilterns and the North Downs. It is one of the sternest shampoo tests in Europe.
• —Some of the hardest urban water in the country is Ipswich (around 435 mg/l), then Hull, Norwich, Luton and Cambridge — all around or above 300 mg/l.
• —By contrast: Glasgow is around 16 mg/l (Loch Katrine), and Edinburgh, Manchester, Birmingham and Liverpool sit in a very soft band. Moving from Manchester to London is, for hair, a change of two orders of magnitude.

Denmark. A small country with large differences. The hardest water sits on Zealand, Falster, Lolland, Møn and Funen. Jutland is generally softer — but not everywhere.

• —Copenhagen — natural hardness in the capital region is typically 18–30+ °dH. Hofor is rolling out central softening: where it is already on, water falls to about 10–12 °dH; other districts can still be hard. More than half of the metropolitan supply is now softened, with the rest staged through to 2031. Two neighbours in Copenhagen can therefore have different hair from the same shampoo.
• —Aarhus — Aarhus Vand reports 11–20 °dH (fairly hard to hard). There is no central softening here.
• —Dragør is among the hardest in the country — above 30 °dH, extremely hard.

France. Hardness is given in French degrees: 1 °f ≈ 10 mg CaCO₃/l.

• —Paris — Eau de Paris / ARS: hydrotimetric titre around 26.5–36.5 °f, roughly 265–365 mg/l. Hard to very hard, in the same league as London.
• —Lyon — clearly softer; ARS analyses often show calcium around 60–70 mg/l, and the water is classed as rather soft to moderate.
• —Nice — a mixed network: depending on the intake, TH often lands around 20–30 °f. The limestone south is more “calcareous” than the Rhône.

Sweden. The two big cities in the north are the opposite of London and Paris.

• —Stockholm — Stockholm Vatten och Avfall: soft water, 4–6 °dH (Lake Mälaren).
• —Gothenburg — Göta älv water is usually very soft.
• —The south, on the limestone of Skåne, can be harder — check the current VA SYD or local utility report. A move from Stockholm to Paris or London is, for hair, a jump across the whole scale.

Germany. Large regional differences. Berlin is among the hardest big cities — values around 24 °dH. Frankfurt am Main up to about 19.7 °dH, Munich about 19 °dH. Hamburg is around 11 °dH, Essen around 6.7 °dH — soft. Formally, “hard” in Germany starts at 14 °dH.

Poland. Water is hard in most large cities:

• —Warsaw — around 17–19 °dH
• —Kraków — depends on the intake: Dłubnia around 296 mg/l, Bielany around 288, Rudawa around 278, but Raba only around 128 mg/l (soft). That is why neighbours in different districts can disagree.
• —Poznań — around 16–18 °dH, higher at some intakes
• —Zamość — above 22 °dH, one of the highest values in the country

The coast (Tri-City, Szczecin) is clearly softer. The south, on Jurassic and Cretaceous formations, is harder.

Italy and the Netherlands, briefly. Rome is often around 200 mg/l (moderately hard to hard). Milan and the Po Valley are usually harder than the Alps. Amsterdam sits in a medium / relatively soft band (often around 8 °dH) — a different story from London.

Always check your water company’s current report — hardness shifts between districts, intakes and seasons. Useful starting points: Thames Water, Hofor, Eau de Paris, Stockholm Vatten, MPWiK Warsaw, Kraków Waterworks, Aquanet.

What hard water does to hair

Calcium and magnesium ions combine with anionic surfactants into insoluble salts that deposit on the cuticle. Effects build over weeks:

• —hair feels rough and looks dull
• —combing is harder, with more mechanical cuticle damage
• —coloured hair fades faster and shifts in tone
• —the scalp itches and flakes more
• —conditioners “stop working” — they cannot reach the fibre through a deposit layer

A separate thread is copper from pipework, which accumulates especially in blonde and grey hair and speeds keratin oxidation.

The BOGDAO approach: chelation during washing

A shower filter works, but it needs installing, cartridge changes, and it does not travel with you. We chose to handle the problem in the formula.

The BOGDAO chelating complex works at the moment of washing — in contact with water, before deposit can form. It has three parts, working at different levels:

Trisodium Ethylenediamine Disuccinate (EDDS) — a biodegradable chelator that binds calcium, magnesium, copper and iron into stable complexes before they meet the hair.

Hardness-resistant surfactants — Sodium Methyl Cocoyl Taurate is a taurate that, unlike classic anionic detergents, does not precipitate in the presence of calcium ions. It still cleanses where ordinary shampoos give dull foam and residue.

Polyglyceryl esters (Polyglyceryl-6 Caprylate, Polyglyceryl-3 Cocoate, Polyglyceryl-4 Caprate, Polyglyceryl-6 Ricinoleate) — a gentle micellar system that keeps soils and bound ions in suspension so they rinse away instead of settling back onto the hair.

Plus an acidic formula pH, which does not encourage the cuticle to lift, and inulin and Hydroxypropyl Gluconamide working on the fibre itself.

Who it is for

Residents of London, Copenhagen, Paris, Berlin, Warsaw, Kraków, Aarhus and any other city above 200 mg CaCO₃/l. People with coloured, bleached and grey hair. Anyone who noticed after a move that their hair “changed for no reason”. And anyone who travels and does not know what water is waiting in the shower.