Dunea water hardness: what is in your water?

Reading time: about 13 minutes

What is Dunea and who gets its water?

Dunea supplies drinking water to almost 1.4 million people in the west of Zuid-Holland (the province of South Holland), twenty-four hours a day. That is stated on Dunea’s own drinking water page, which also expects growth to around 1.6 million residents by 2040. Den Haag (The Hague) and Leiden lie right in the middle of that area, which explains why so many searches about water hardness come from there.

That makes Dunea one of the ten drinking water companies in the Netherlands. Which company serves your street determines the composition of your tap water, because each company uses a different source and a different treatment process. If you want to see what that map looks like nationally, you will find it in our overview of where our drinking water comes from.

Where does Dunea’s drinking water come from?

Dunea makes drinking water from river water. The first source is the Afgedamde Maas, a side branch of the Maas (Meuse) that flows slowly and has a strong self-cleaning capacity; the second is the Lek. That is how the company describes it on its drinking water page. This puts Dunea in the minority: according to the RIVM (the Dutch National Institute for Public Health and the Environment), about 60 per cent of Dutch drinking water is made from groundwater, and the rest from surface water.

The dunes as an extra purification step

The river water does not go straight into the pipes. Dunea manages the dune areas of Berkheide, Solleveld and Meijendel, and describes the infiltration ponds in Meijendel as important for water extraction. There, the water seeps through the dune sand before it is pumped up again. That detour through the ground is the reason the company used to be called Duinwaterbedrijf (dune water company) and why people still search for dune water.

For its pipe network, Dunea uses four types of pipe: a raw water transport main, a drinking water transport main, a distribution main and the service pipe to your home. That last one stops at your water meter, and that is exactly where your own responsibility begins. More on that further down.

How hard is Dunea’s water exactly?

The water Dunea supplies has a hardness of about 1.42 mmol/l, which equals 7.9 degrees of German hardness. Dunea states that figure itself on its page about water hardness, and it also appears in the hardness table on that same page: 4 to 8 degrees of German hardness, or 0.71 to 1.43 mmol/l, is called soft water. At 7.9, Dunea sits at the top of that class, but still within it.

That is no coincidence. Dutch drinking water companies soften the water centrally, before it reaches your home. Dunea does this too. As a result, truly hard water, like you find in parts of Germany or Belgium, hardly occurs in the Netherlands any more. How hardness varies by region and why one municipality sees more limescale than another is covered in our article on how hard tap water is per municipality.

Note the lower limit on the other side. Under the Drinkwaterbesluit (the Dutch Drinking Water Decree), the hardness in your indoor installation may not drop below 5.6 degrees of German hardness, which is the same limit as the legal 1 mmol/l. Water without calcium and magnesium is aggressive towards pipes. Anyone who installs a water softener in the Dunea area therefore has only a narrow margin to gain: from 7.9 to 5.6 at most.

What do you notice from 7.9 degrees of German hardness?

Three things, and all three are mild.

• Less detergent: softer water needs less soap and less washing and washing-up detergent. Dunea itself names this as the practical advantage of soft water. So check the soft water dosage on the packaging, because the standard dosage often assumes harder water.
• Limescale, but slowly: 7.9 degrees is soft, not zero. Your kettle and your shower screen still get a white film, it just takes longer than in a region with 12 degrees. How to deal with that is covered in our article on removing limescale and in the explanation of why your kettle scales up.
• Hot water is a separate story: limescale precipitates faster the hotter the water is. Dunea advises not to set hot water appliances too low: at least 60 degrees, because otherwise bacteria get a chance.

For removing limescale deposits, Dunea refers to ordinary cleaning vinegar, with the note that you follow the manufacturer’s cleaning instructions first. That is more affordable and simpler than most descalers on the shelf, and more than enough for 7.9 degrees. If you want to know what a filter does and does not change about this, read what a water filter does with limescale.

Does Dunea’s water hardness vary by postcode?

Here is a difference from most other drinking water companies, and it is worth knowing. Many companies offer a postcode check because they supply from several extraction sites with different hardness levels. On its hardness page, Dunea mentions no difference at all by postcode: there is one value for the supply area, and that is 1.42 mmol/l.

In practice, that means the following. Whether you look up the water hardness in Den Haag, in Leiden, in Zoetermeer or in Delft, you arrive at the same 7.9 degrees of German hardness, as long as you live within Dunea’s supply area. So you do not need to enter a postcode to determine your dosage.

If you are unsure whether your address belongs to Dunea, for example because you live right on the border with the area of Evides or Oasen (two other Dutch drinking water companies), the quickest check is your own water bill. If another company is listed, read our article on water quality at Evides or on Oasen’s drinking water. If you simply want to measure it yourself, you can do so with a test strip; how that works is explained in measuring water hardness at home.

Is there PFAS in Dunea’s drinking water?

Start with the standard, not with a feeling. According to the RIVM, the sum of twenty different PFAS in drinking water may be no more than 100 nanograms per litre, and Dutch drinking water meets that. In addition, the RIVM advises a stricter guideline value of 4.4 nanograms per litre, expressed in PFOA equivalents for the whole mixture. That 4.4 is not law, but health advice.

Two statements from the RIVM are especially relevant for Dunea customers. The first: drinking water made from groundwater contains less PFAS than drinking water made from surface water. Dunea works with river water, so that is the category with the higher starting level. The second: average intake via drinking water alone stays below the health-based limit, but intake via food is about three times as high, and together food and drinking water do exceed it.

Dunea itself writes that traces of substances from consumer use, industry, agriculture and land use can occur in drinking water, in very low concentrations, and that if an exceedance is expected at the source, the company reports it to Rijkswaterstaat (the Dutch public works and water management agency) and takes measures. That is exactly how it should work, and it is also why the Maas is in the news from time to time: when there is pollution, intake is temporarily stopped.

What you should make of that depends on how much margin you want yourself. The legal standard is met. If you want to get closer to the RIVM advisory value, that is a choice you make at home, not a shortcoming of your water company. How the different techniques compare on this point is covered in which technique filters PFAS best and in the background piece on PFAS as forever chemicals. The PureFilter Mineral+ removes 83% to 85% of PFAS from tap water, including PFOA and PFOS, measured by an independent lab.

Chlorine, pharmaceutical residues and taste

First, a persistent misconception: Dutch tap water contains no chlorine. The RIVM states this in so many words, and adds that its quality is among the best in the world. So if you taste a chemical aftertaste in Den Haag or Leiden, you are tasting something other than chlorine. That saves a lot of searching.

What you are actually tasting

Usually it is temperature or stagnation. Water that has stood in the pipe all night is lukewarm and tastes flat; water that has just come from the cold pipe tastes fresher. We describe that effect in the ideal temperature of tap water. A metallic taste points more to your own plumbing, and that route is covered in why tap water tastes of iron.

Pharmaceutical residues and other micropollutants simply occur more often in surface water than in deep groundwater. That is why companies that work with river water invest in extra purification steps. It is no reason to panic and certainly no reason to switch to bottled water: by every calculation we have made, that costs dozens of times more per litre, as you can see in what a cubic metre of tap water costs.

What Dunea cannot control: your own pipes

A drinking water company’s responsibility runs up to the water meter. Everything beyond it is your indoor installation, and that is where most of what people complain about happens. Three points that often come up in the west of Zuid-Holland, with a lot of pre-war housing in the city centres:

• Old pipe materials: homes built before 1960 may still contain lead pipe sections. How to recognise them without demolition work is explained in recognising lead pipes.
• Stagnation in long pipes: flats with long risers more often have lukewarm water when you first run the tap. Flushing helps, and it is also the reason that legionella in shower pipes in particular is a point of attention.
• Boiler set too low: economical heating sounds sensible, but Dunea explicitly names a minimum of 60 degrees so that bacteria do not get a chance.

A water softener of your own is rarely the solution in this area, and it does not come without obligations. Dunea sets requirements: a Kiwa ATA certificate or equivalent, an accredited installer and the InfoDWI regulations. Such a device can also cause a pressure loss of about 70 kPa, which is 0.7 bar. If the correct non-return valve is missing or the device is not connected properly, Dunea can require the connection to be modified or the device to be removed, at the customer’s expense. The company deliberately gives no advice on suppliers or products.

Do you need a water filter in the Dunea area?

The honest answer has two parts, and the first part sells nothing.

Not for the hardness

A water filter is not a water softener. Neither is the PureFilter Mineral+: it does not lower the hardness of your water and does not prevent limescale in your kettle, on your shower screen or in your washing machine. At 7.9 degrees of German hardness that is no loss either, because soft water causes those complaints less often anyway. If you only want to tackle limescale, you need a different device; the difference is explained in water softener or water filter.

But for taste and for substances that do not exceed any standard

This is the real question. Dunea’s water meets the legal standards, but meeting a standard is something other than zero. A filter on the cold water pipe is an extra margin you choose yourself, on top of what your water company already does. The PureFilter Mineral+ filters all 40 chemicals tested, from 75% to 99.97%, tested by Equinox Labs, independent laboratory (2026). Lead, mercury, arsenic and cadmium are reduced to below the detection limit, and nitrate by 99%.

Then something else happens. In the final filter stage, Swedish Mineral Rock™ adds calcium, magnesium and potassium, so the water does not come out bare. That is the difference from a reverse osmosis system, which removes everything and then has to add it back. At PureFilter, we see that customers mainly choose for taste and convenience, not for descaling. We set out which technique does what side by side on the types of water filters at a glance.

If you live in the Dunea area and have a Quooker, pay attention to the order: the filter belongs on the cold water supply, so before the Quooker tank. This is explained in detail on our page about a water filter alongside a Quooker. If you first want to see what fits under your sink in terms of size, take a look at the fixed filters that refine the taste of your tap water.

Comparison: what the options deliver

Buying advice in brief

Choose based on your own complaint, not on a figure from a brochure.

• Only limescale: do nothing special. At 7.9 degrees, occasional cleaning vinegar is enough, exactly as Dunea advises.
• Taste, or a margin on substances: then a fixed filter on the cold water pipe is the logical step. It filters the moment you run the tap, so you do not need to refill anything or put anything in the fridge.
• Rented home or unsure about fitting: installation takes 5 to 10 minutes and requires a pair of water pump pliers, not a plumber. The steps are in our guide to connecting a water filter.
• Compare first: if you want to see brands side by side, start with our comparison of the best water filters or with the separate Brita water filter review.

There is little to surprise you in the costs. The unit costs €149.00 including the first filter. A single replacement filter is €65.00 and lasts up to 12 months for 1 to 3 people, and up to 6 months for 4 or more. If you would rather not think about it, you can also use the Filter Plan: €48 per year for 1 to 3 people. How much water you actually send through such a filter depends on your household; we calculate that in average water consumption per person and in how much water you need per day.

Frequently asked questions

Conclusion

Dunea water hardness is 1.42 mmol/l, or 7.9 degrees of German hardness, and that applies to the entire supply area in the west of Zuid-Holland. That is soft water, and it is also the most boring part of this story: you do not need a water softener for it, and cleaning vinegar will get you a long way.

What lies above and below it is more interesting. Dunea makes drinking water from river water and lets it seep through the dunes, and the RIVM notes that drinking water made from surface water contains more PFAS than drinking water made from groundwater. The legal standard is met; the stricter advisory value of 4.4 nanograms per litre is a trade-off of your own. And the stretch of pipe between your water meter and your tap is entirely yours.

If you want to build in a margin of your own over those last few metres, a fixed system filters the moment you run the tap. What that looks like, what it costs per year and which warranty comes with it can be found on purefilter.nl; practical questions about fitting and maintenance are answered in the frequently asked questions, and the replacement schedule in our article on how often to replace a water filter.