Frequently asked questions
Water hardness, the planner, and how this site works, in plain answers.
What is water hardness?
Water hardness is the amount of dissolved calcium and magnesium in tap water, picked up as the water moves through rock and soil. It is measured in milligrams per litre (mg/L) as calcium carbonate, and it is the single biggest reason the same hair routine behaves differently from one city to the next. Our explainer walks through it: How hardness is measured.
How is hardness measured, and what are the four bands?
The common currency is mg/L; France also uses degrees French (°f) and Germany degrees German (°dH), with 1 °f equal to 10 mg/L. We band every city the same way: soft under 60 mg/L, moderate 60 to 119, hard 120 to 180, and very hard over 180. The full scale, with what each band does to hair, is at How hardness is measured.
Where do the city figures come from, and how often are they checked?
Each of the 360 figures comes from the utility or authority that publishes that city’s supply wherever one exists, and every city page and plan names its source and confidence level: official, published or estimate. Cities whose utilities publish no citable figure are left out rather than guessed. The whole set is re-checked against its sources every week, and any figure that has moved is reviewed before it changes here.
What does hard water do to hair?
Minerals in hard water coat the strand wash after wash: hair goes dull, tangles more, feels rough, and colour fades faster, especially on porous or bleached hair. It is build-up, not damage from a single wash, which is why the fix is a rhythm of detox washes rather than a stronger everyday shampoo. Read more: Hard water, explained.
What does chelating mean?
Chelating (a detox wash) means using a formula with ingredients that bind to mineral ions and lift them off the hair, instead of just washing over the top of them. It is the specific tool for hard water build-up, used every few washes rather than daily. Read more: Hard water, explained.
How does the trip planner work?
Tell it your home city, your hair profile (texture, colour treatment, how you dry it) and your stops in order, with the month for each. It compares every destination’s water with your home water and builds a washing rhythm, a chosen kit of real products with buy links for your country, and one merged packing list, then emails the plan to you from your own mail app. Start here: Plan your good hair trip.
How does this site make money?
Some product links on this site are affiliate links. A service called Skimlinks runs on the site and turns eligible outbound product links into affiliate links, and some links are placed with affiliate networks and retailers directly. If you click through and buy, we may earn a commission at no extra cost to you; recommendations are our editorial picks either way. The full wording is in our Privacy page.
Do I need an account, and what do you store?
No: the planner works without one. An account simply saves your hair profile and your trips so they are there next visit, with passwords stored as salted hashes, never in plain text. The owner view of account data is aggregated only, with no member names or emails. Details: Privacy page and your account.
What is the newsletter?
A short email about once a month: new cities, water maps and Journal pieces. It runs through MailerLite with double opt-in, so you confirm by email before anything is sent, and every issue carries an unsubscribe link. Your plan emails are never added to it unless you tick the newsletter box yourself. Sign up in the footer of any page.