Water hardness in Groningen: how hard is your tap water?

Reading time: ~12 minutes

How hard is the tap water in Groningen?

Waterbedrijf Groningen itself gives one range for its entire supply area: 6 to 12.5 degrees of German hardness. That is not a sloppy estimate but a consequence of how the company works. The water in your tap does not come from a single well but from several production sites, and which site supplies your neighbourhood at any given moment varies. That is why the company publishes the maximum hardness per postcode instead of a single provincial average.

To put that range in context: according to the Drinkwaterplatform, the Dutch average is around 8 °dH. Groningen is therefore partly below and partly above it. If you live in the softest part of the area, your water leaves hardly any limescale. If you live in the hardest part, at 12.5 °dH you are well above the national average and you notice it every week in your kettle.

That difference within a single province is exactly why a national map tells you little. If you want to know where your address stands, look at the water hardness per municipality and then enter your postcode with your own drinking water company. That is the only measurement that really applies to your tap.

Why one source says soft and another says fairly hard

Search for water hardness in Groningen and you will come across contradictory terms. One site calls the same water average, another fairly hard, and a third says it is simply soft. That is not because anyone is mistaken, but because the Netherlands has no official hardness scale. The Drinkwaterplatform notes that the ten drinking water companies use five different scales between them.

Waterbedrijf Groningen uses this classification:

That last row is more important than it looks. Waterbedrijf Groningen states in so many words that water above 18 °dH does not occur in the Netherlands. What adverts for softening equipment call hard water therefore falls, in this area, into the categories soft, average or at most fairly hard. That difference decides whether you have a problem or just a cleaning job.

There is also a legal floor. The Drinkwaterbesluit (the Dutch Drinking Water Decree) does not allow drinking water companies to soften below 5.6 °dH. Vitens (a Dutch drinking water company) calls that the minimum hardness softened water must retain. Completely limescale-free tap water therefore does not exist in the Netherlands, and that is deliberate: water that is too soft can leach metals from pipes. You can read more about this in our overview of hard water in the Netherlands.

Where Groningen’s drinking water comes from

The hardness of your tap water is no coincidence. It comes straight from the ground where the water was abstracted, and in that respect Groningen is an exception. Waterbedrijf Groningen supplies around 44 billion litres of water a year and uses two types of source at the same time to do so. By no means all drinking water companies do that.

Groundwater from the Drents Plateau

The largest share, around 37 billion litres a year, is groundwater pumped up in water abstraction areas on the Drents Plateau. That water has seeped through layers of sand for years, picking up calcium and magnesium along the way. It is precisely those minerals that determine the hardness. Treatment is relatively simple: aeration in a pre-filter removes iron and ammonium, aeration in a post-filter removes manganese, and the water then goes into the clean water reservoirs.

Surface water from the Drentsche Aa

In addition, a good 7 billion litres a year comes from the Drentsche Aa, a stream. Surface water needs much more treatment. Waterbedrijf Groningen describes eight steps: a screen against coarse debris, a mixing basin where the water stays for an average of 60 days so that fluctuations in turbidity and temperature are smoothed out, coagulation with a flocculant, dual-layer filtration over anthracite and sand, activated carbon filtration, UV disinfection against micro-organisms, a final filter with aeration via a cascade, and only then storage.

Two things follow from this. First: because your neighbourhood can be supplied with groundwater at one time and with a blend at another, the hardness varies within the area. Second: the activated carbon filter in the surface water treatment works on the same principle as a household filter, just on an industrial scale. That is no coincidence, because activated carbon is simply the technique that removes taste, odour and organic substances from water. We have set out which filter type does what on our page about which filter type suits moderately hard groundwater.

From the clean water reservoirs, the water enters a pipe network of around 5,200 kilometres. At every stage, the WLN laboratory takes samples. That fits a national picture: according to Vewin (the association of Dutch drinking water companies), 99.9 per cent of all measurements meet the legal quality standards, and drinking water in the Netherlands is monitored more strictly than food. If you want to see the whole journey from source to glass, read where our drinking water comes from.

Is hard water in Groningen unhealthy?

No. This is the point where most search results confuse you, because the pages that rank highly on this topic nearly all sell softening equipment. The sources without a commercial interest are unanimous.

Waterbedrijf Groningen states that hard water is not unhealthy and that calcium and magnesium are actually useful for building bones. Vitens reaches the same verdict and adds that the taste is fine. The Drinkwaterplatform goes a step further and reports that hardness has virtually no effect on health, and that older concerns about a link between soft water and heart failure turned out to be negligible in scientific research.

The RIVM (the Dutch National Institute for Public Health and the Environment) sums up the broader question briefly: tap water in the Netherlands is so clean that you can drink it without worry, and its quality is among the best in the world. That applies in full to the water that comes out of the tap in Groningen.

Remarkably, the health argument is if anything on the other side. The Drinkwaterplatform points out that soft water is more likely to irritate the skin, because soap rinses off less easily, and that water that is too soft with a low pH can leach metals from pipes. Van Pol of WML (the drinking water company in Limburg) puts it like this: limescale in the water actually creates a kind of protective layer on the inside of the pipes.

What you notice of this hardness at home

Limescale is not dirt coming out of your tap. It only forms when the water is heated: calcium then reacts with carbonate to form calcium carbonate, which settles on the first warm surface it meets. That is how Vitens explains it, and it also explains why you see it in your kettle and on your shower screen, and not in the cold water pipe.

At 6 to 12.5 °dH, in practice that means:

• Kettle: a white layer on the heating element, after a few weeks to a few months depending on your neighbourhood. How to deal with it is covered in our piece on descaling your kettle.
• Shower and taps: white spots on glass and chrome. See descaling your shower head for the routine that suits your hardness.
• Washing machine and dishwasher: Waterbedrijf Groningen recommends washing below 60 degrees and notes that you do not need softening powder, though you do need a little more detergent.
• Energy use: the Drinkwaterplatform points out that limescale lowers the efficiency of appliances, increases energy use and leads to faster breakdowns.
• Glassware: a dull film on glasses, which has to do with limescale and not with your dishwasher detergent.

The practical tips from the drinking water company itself are surprisingly mundane: clean appliances more often with cleaning vinegar, squeegee tiles and the shower screen dry, and wash at a lower temperature. You will find more ways to remove deposits in removing limescale.

There is another side that is often forgotten: limescale costs money in the form of water and energy, not in the form of your water bill. We have calculated what you pay per cubic metre in what a cubic metre of water costs.

Water softener or water filter: what does what?

This is where most of the confusion lies, and where we have to be honest about our own product.

So what does a softener do? Waterbedrijf Groningen describes the process soberly: the softener usually removes the limescale completely, but converts calcium into sodium. The company cites the recommended sodium intake of 1 to 1.5 grams a day, and points to two risks: bacterial growth that can affect odour and taste, and an interruption of the direct water supply to the taps. Maintenance, cleaning and regeneration are your own responsibility.

And is it necessary? The Drinkwaterplatform reports that the Consumentenbond (the Dutch consumers association) and its European sister organisations only advise households to soften their own water above 20 °dH, and notes that Dutch tap water is practically never that hard. With an upper limit of 12.5 °dH, Groningen is well below that. We see this with customers too: anyone who calls about limescale almost always benefits more from a descaling routine than from an appliance costing thousands of euros.

If you are torn between the two, our comparison water softener or water filter will help you further. If you first want to know exactly where you stand, measure your hardness yourself: measuring water hardness at home compares the test strip, the drop test and the postcode check side by side.

What a water filter does remove from Groningen tap water

If a filter does not tackle limescale, why would you fit one in Groningen? For a different reason than most people think, and it is more honest to simply name that reason.

Milieu Centraal (the Dutch consumer organisation for environmental issues) explicitly advises against using a water filter, because it is not necessary given the high quality of Dutch drinking water, and warns that quality can even deteriorate if bacteria start growing on the filter. The same warning comes from TU Delft professor Jan Peter van der Hoek, who says in the Drinkwaterplatform piece that every extra filter on a tap can act as a bioreactor. That criticism is valid, and it applies to every filter that is not replaced in time.

What an under-sink filter does do is bring the water further down than the legal standard requires, and refine the taste. The filter we fit under the sink works in five layers: a pre-filter, two layers of carbon fibre, Swedish Mineral Rock™ and a post-filter. The measured results, by Equinox Labs, independent laboratory (2026):

• Chlorine: no chlorine taste, no chlorine odour, 99.97 per cent less chlorine.
• PFAS: 83 to 85 per cent less PFAS, including PFOA and PFOS.
• Heavy metals: lead, mercury, arsenic and cadmium reduced to below the detection limit.
• Nitrate and fluoride: 99 per cent less nitrate and 94 per cent less fluoride.
• Microplastics: the carbon block has very small pores, so larger particles get caught.
• Minerals: Swedish Mineral Rock™ adds calcium, magnesium and potassium in the final step.

Two limits belong right alongside that. The filter does not disinfect: if your drinking water company issues a boil-water advisory, you follow that advice. Full stop. And it does not change the hardness, as stated above. At PureFilter we see that customers in Groningen mainly choose it for the taste and because of PFAS, rarely because of limescale, and that is exactly the right expectation.

In practical terms: the Mineral+ costs €149.00 including the first filter, and a single replacement filter €65.00. If you would rather not have to think about it, you can also use the Filter Plan, from €48.00 per delivery for 1 to 3 people. How long a filter lasts depends on your household: up to 12 months for 1 to 3 people, up to 6 months for 4 or more. You connect it to the cold water pipe yourself in 10 minutes, with a single pair of water pump pliers, even if you have a Quooker (a boiling-water tap). If you want the bigger picture first, take a look at the best water filter or at our range of water filters.

Frequently asked questions

Conclusion

The water hardness in Groningen is between 6 and 12.5 degrees of German hardness, and exactly where you sit depends on your postcode and on which production site supplies your neighbourhood. That is because Waterbedrijf Groningen uses both groundwater from the Drents Plateau and surface water from the Drentsche Aa. The entire range falls below the 20-degree threshold above which a softener is recommended at all, and well below the 18 degrees the drinking water company itself calls hard.

In practice that means: you have limescale, not a problem. Descale your kettle and shower head on a routine that suits your value, squeegee your shower screen dry and wash below 60 degrees. A softening system is rarely worth it for this water, and the drinking water itself is safe as it is.

If you still want to do something about your water, distinguish between limescale and content. Limescale calls for a softener or a cloth. Taste, chlorine, PFAS and heavy metals call for a filter. We can help you with that, and honestly not with limescale. You will find more background on purefilter.nl and in our frequently asked questions.