Short answer
Start with the water supplier's published water quality data. In the EU, hardness is on the list of information that must be accessible to consumers online, and in England and Wales the regulator advises asking the water company for an accurate figure. Record hardness in mg/L as calcium carbonate before you compare markets: dividing by 100 gives mmol/L.
Before you decide which shower filter version to stock, you need one number that most buyers do not have yet: how hard the tap water is in the places you plan to sell. Hardness data exists for many cities, but it is rarely sitting in one table, and the way it is reported changes from one country to the next.
This guide shows where to look, how to read the figure once you find it, and what the number can and cannot tell you when you choose between a Basic and a Limescale version.
Start with the supplier's published data
Many water suppliers publish water quality data online, but what they must publish depends on the market.
- European Union. Directive (EU) 2020/2184 on drinking water lists the information that must be accessible to consumers online. Its Annex IV includes recent monitoring results and information on hardness and on dissolved minerals such as calcium and magnesium. In Germany, the detergents law (WRMG) also requires water suppliers to tell consumers the hardness range of their water at least once a year.
- England and Wales. The Drinking Water Inspectorate (DWI) publishes a hardness map, but advises asking the water company directly for an accurate measurement, because some areas have local variation that the map does not show.
- Australia. Sydney Water's online water analysis tool shows total hardness for an address. Water Corporation in Western Australia publishes a drinking water quality annual report for each region.
If a supplier serves several areas, ask which figures apply to the address you care about.
Hardness may not be in the report
This is where many searches stall outside the EU. Drinking water standards are built around parameters that matter for health, and hardness is usually not one of them. The DWI notes that the regulations for England and Wales do not specify standards for hardness, calcium or magnesium, and Health Canada concluded that a health-based value for hardness is not warranted.
So where the law does not require it, each supplier decides whether and how to show it. Some put it in a table of additional or aesthetic parameters, some give it on a separate page, and some leave it out. When you open a report, search for these words:
- hardness
- total hardness
- calcium
- magnesium
- CaCO3
If none of them turn up, ask the supplier directly.
Read the unit before you compare markets
Most suppliers report hardness in milligrams per litre (mg/L) as calcium carbonate (CaCO3), sometimes written as ppm. Appliance makers and some European sources use millimoles per litre (mmol/L), and you will also meet German degrees (dH) and French degrees (fH).
Sydney Water's conversion between the first two is simple: divide mg/L by 100. Greater Sydney's water, at about 57 mg/L, is about 0.57 mmol/L. Sydney Water's analysis tool also lists hardness in ppm, dH and fH, so when a supplier publishes a degree figure, use that figure rather than converting it yourself.
The labels differ more than the units:
| Source | Soft | Middle bands | Hard | Very hard |
|---|---|---|---|---|
| DWI and Thames Water (England) | Up to 100 mg/L | Slightly hard 100 to 150 mg/L; moderately hard 150 to 200 mg/L | 200 to 300 mg/L | Over 300 mg/L |
| Germany, detergents law (WRMG) | Under 1.5 mmol/L (about 150 mg/L) | Medium 1.5 to 2.5 mmol/L (about 150 to 250 mg/L) | Over 2.5 mmol/L (about 250 mg/L) | Not used |
| Sydney Water (Australia) | Under 60 mg/L | Not used | Over 60 mg/L | Not used |
Health Canada's technical document adds that hardness above 200 mg/L is considered poor but has been tolerated by consumers, and that more than 500 mg/L is unacceptable for many domestic purposes.
A competitor's box that says "for hard water" may be using any of these scales. When you collect data for several countries, write down the figure in mg/L as CaCO3 and keep the supplier's own label as a separate note.
If a report shows a range instead of one number, ask the supplier what the range covers and whether it applies to the address in question.
What hardness looks like at the shower
The DWI explains that water hardness is caused by dissolved calcium and magnesium. Two things happen when that water reaches a shower.
First, soap. The DWI says hard water produces less lather from soaps, and Health Canada describes hard water as needing a considerable amount of soap to produce a lather.
Second, heat. Hardness minerals can come out of the water as deposits. The DWI lists scaling in hot water systems, kettles, irons and domestic appliances, and Thames Water describes the chalky residue that hard water can leave behind as limescale. It is the same crust that forms around the nozzles of a shower head.
Hardness itself is generally treated as a nuisance rather than a health risk. Thames Water says hard water is not considered harmful.
When supplier data does not apply
Two situations make a supplier's figure a weak guide:
Private supplies. Wells, boreholes and springs that are not connected to a public supplier are not covered by a supplier's published data. In a market with many private supplies, a home test kit or a water testing laboratory is the only way to get a number.
Water treated after the supplier. Some suppliers soften water before delivery, and a building may treat it further. If you need the hardness at the shower itself, test there with a suitable kit or ask a qualified laboratory.
Using the number to choose a version
Water Healer travel and large-capacity sets come in a Limescale version. Limescale versions add an ion-exchange stage designed to help manage scale-forming minerals in harder water. A hardness figure is a sensible reason to put that version first on your sample list.
Keep three limits in mind when you talk to customers:
- A shower filter treats water at one fixture. It is not a whole-house softener, and it should not be described as one.
- Do not promise that very hard water will become soft. Higher hardness can mean more scale, but how fast it appears also depends on temperature, use and cleaning.
- Hardness does not predict a replacement date. Our replacement periods are guidelines, and a cartridge may need replacing two to three times sooner depending on water quality and usage.
KTR issued a calcium, magnesium and total hardness test report on a Water Healer filter sample in August 2026. We share it with qualified buyers on request and do not publish the figures on this website. The Quality page lists what we can document today.
A short checklist for each market
- Find the water quality data for your three largest target cities.
- Record hardness in mg/L as CaCO3, with the source and the year. Add mmol/L if your customers' appliances use it.
- Note whether private supplies or building softeners are common.
- Decide which version to sample first: Basic or Limescale.
- Send the figures with your quote request so we can discuss samples against real water data.
FAQ
Does a water supplier publish hardness?
In the EU, Directive (EU) 2020/2184 lists hardness among the information that must be accessible to consumers online. Elsewhere it depends on the supplier. Search the report for "hardness," "calcium" or "CaCO3," and if it is not there, ask the supplier. In England and Wales, the DWI advises asking the water company directly for an accurate figure.
How do I convert mg/L to mmol/L?
Divide by 100. Sydney Water gives the example that 57 mg/L is 0.57 mmol/L. If a customer's appliance asks for German or French degrees, use the figure the supplier publishes in that unit.
Does a hard-water market need the Limescale version?
Not automatically. Hardness is one input. The Limescale version adds an ion-exchange stage designed to help manage scale-forming minerals in harder water, and results depend on water conditions and use. Tell us your market data with your quote request and we will discuss which version to sample.
Is hard water a health concern?
Hardness itself is generally treated as a nuisance rather than a health hazard. The DWI notes that the regulations for England and Wales set no standard for hardness, and Health Canada says a health-based value is not warranted. A hardness figure does not tell you whether the water meets other drinking water standards, so use the full water report for those questions.
Sources
- European Union, "Directive (EU) 2020/2184 on the quality of water intended for human consumption" (Annex IV): https://eur-lex.europa.eu/eli/dir/2020/2184/oj
- Germany, "Wasch- und Reinigungsmittelgesetz (WRMG), § 9": https://www.gesetze-im-internet.de/wrmg/__9.html
- Drinking Water Inspectorate (England and Wales), "Water hardness": https://www.dwi.gov.uk/consumers/learn-more-about-your-water/water-hardness-hard-water/
- Thames Water, "Hard water": https://www.thameswater.co.uk/help/water-and-waste-help/water-quality/hard-water
- Sydney Water, "Drinking water analysis": https://www.sydneywater.com.au/water-the-environment/how-we-manage-sydneys-water/safe-drinking-water/water-analysis.html
- Water Corporation (Western Australia), "Water quality": https://www.watercorporation.com.au/Help-and-advice/Water-quality
- Health Canada, "Guidelines for Canadian Drinking Water Quality: Guideline Technical Document, Hardness": https://www.canada.ca/en/health-canada/services/publications/healthy-living/guidelines-canadian-drinking-water-quality-guideline-technical-document-hardness.html
General information only. Water supplies and rules differ by country and by city. Confirm local figures with your water utility or authority.
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