Water hardness testing: how to measure it at home

Reading time: ~9 minutes

What exactly is water hardness?

Water hardness is nothing more than the amount of calcium and magnesium naturally present in your water. Those minerals come from the soil: when groundwater runs through chalky layers, it picks up calcium and magnesium along the way. The more of it in the water, the harder the water is said to be.

One important detail that is skipped almost everywhere: limescale is not present as limescale in your tap water. Vitens (a Dutch water company) explains that limescale only forms when calcium reacts with carbonate, and that this reaction starts as soon as you heat water. That is why you see limescale in your kettle, your shower head and your dishwasher, and not in a glass of cold water. You can read more about this in our piece on filtering limescale out of tap water.

How do you measure water hardness at home? Four methods

1. The test strip (fastest, about two minutes)

You hold a strip in a glass of cold tap water for a few seconds, shake it dry and compare the colour change with the colour chart on the packaging within half a minute. Test strips cost roughly €1.50 to €10.00 and are sold in DIY stores and online. Important: let the tap run for half a minute first, so that you measure the water from the mains and not the water that has been standing in your own pipe for hours.

Drawback: you read off a colour, and colours sit close together. For the difference between 7 and 9 °dH a strip is too coarse.

2. The drop test or titration (most accurate at home)

With a drop test you fill a tube up to a marker with tap water and add a reagent drop by drop, until the colour switches from red to green. Every drop stands for 1 °dH, so you simply count the number of drops. A test kit costs roughly €8.00 to €15.00 and lasts dozens of measurements.

This is the most accurate do it yourself method and the only one with which you can reliably record a change, for example before and after fitting a softener.

3. The figure from your water company (free, and the most exact)

This is the method most people forget, even though it costs nothing and is the most accurate. Every Dutch water company publishes the hardness of the water it supplies, usually by postcode or town. That value comes from a laboratory, not from a colour chart.

A few examples of what the companies report themselves: Waternet (the water company for Amsterdam and the surrounding area) supplies 7.8 °dH (1.40 mmol per litre) to all of its customers in Amsterdam and the surrounding area. At Brabant Water (the water company for the province of North Brabant) the drinking water is at most 11.2 °dH, with an average that varies from 5.0 to 11.2 °dH by location. In Groningen the hardness lies between 6 and 12.5 °dH according to Waterbedrijf Groningen (the water company for the province of Groningen). We have collected the values per region in our overview of water hardness per municipality.

4. The TDS meter (measures something other than you think)

A digital TDS meter measures the conductivity of water and converts that into the total of dissolved solids in ppm. Handy for seeing that there is something in your water, but a TDS meter does not measure hardness: it also counts sodium, nitrate, sulphate and chloride. A high TDS value can therefore come from salt just as easily as from limescale. Use it as an indication, never as a hardness measurement.

Which method is best for you?

The practical order: first look at what your water company reports, and then measure yourself if you want to know whether your own pipework or a softener still changes anything. At PureFilter we see that customers mainly start measuring themselves after finding limescale in a new appliance and wanting to know whether that is down to the water or to the appliance.

What does your result in °dH mean?

There is no official hardness scale in the Netherlands, and that is not a detail: the Drinkwaterplatform reports that water companies use five different scales. The classification below is however the most widely used and is published in this form by Brabant Water and Waterbedrijf Groningen among others.

The Dutch average sits at around 8 °dH, confirmed by both the Drinkwaterplatform and Waternet. In other words: most people in the Netherlands sit exactly on the border between soft and average. If you want to know how your province compares, we set that out in our overview of hard water in the Netherlands by province.

The misconception: no, 4 °dH is not hard water

This is probably the most important thing you will take away from this article. On many websites that sell water softeners you read that water above 4 °dH is already hard. Waternet calls that incorrect in plain terms and states: water is only hard from 12 °dH upwards.

The Consumentenbond (the Dutch consumers association) and its European sister organisations advise households to start softening only at a hardness of more than 20 German degrees. Such values barely occur in Dutch drinking water any more. So if you measure 9 °dH, you have average water and no problem.

From which value do you see limescale in the house?

For most people visible build up starts at around 8 to 10 °dH, and then mainly in places where water evaporates or is heated: the shower screen, the tap spout, the heating element of the kettle and the dishwasher. Above 12 °dH it happens faster and you also notice it on glassware that turns dull.

Two practical things you can do straight away with your measurement:

• Setting the dishwasher: enter the measured °dH in the water hardness setting. If it is set too low, you get white films on your glasses; if it is set too high, you use unnecessarily much salt.
• Descaling the coffee machine: match the descaling interval to your value instead of to the factory setting. More about this in our piece on the water filter for a coffee machine.

What a water filter does and does not do about hardness

Here we are honest, even when it sells us nothing. A water filter is not a water softener, and neither is the PureFilter Mineral+. Anyone who measures their water hardness, comes out at 14 °dH and wants to be rid of the limescale needs a softener, not a filter. We do not sell softeners and in that case we advise you to look elsewhere.

What a good filter does do is something different, and for many people more important. It takes the substances out of your drinking water that do not belong there: PFAS, microplastics, heavy metals such as lead and copper, pharmaceutical residues, nitrate and chlorine. Hardness is about minerals that are in fact allowed to be there. Those are two different questions, and confusing them is the reason people buy the wrong appliance.

The PureFilter Mineral+ addresses the first question. It is a compact filter that you fit to the cold water pipe under your sink, with five filter stages that remove more than 100 contaminants, and a final stage with Swedish Mineral Rock™ that gives calcium, magnesium and potassium back. It is NSF certified to 42, 53, 61 and 372. Installation takes 5 to 10 minutes: you do not need a plumber, for the installation you use one pair of water pump pliers, and you change the cartridge later with the supplied key. Our guide to installing a water filter sets out step by step how that works.

If you are unsure which type suits your situation, first look at the different kinds of water filters and how they work before you buy anything. And if you have a boiling water tap, read why a Quooker does not filter the water, because that is a persistent misconception.

Softener, filter jug, osmosis or under sink filter

The cost per litre varies far more than the purchase price suggests. A replacement filter costs €65.00 and lasts 15,000 to 20,000 litres, which works out at less than one cent per litre, against €0.40 to €1.00 for a litre of bottled water. How that compares with the price of tap water itself is something we work out in our article on what a cubic metre of water costs.

If you want to see what actually fits under a sink, take a look at a fixed filter on the cold water pipe in our range.

Frequently asked questions

Conclusion

Testing water hardness takes you two minutes and need not cost anything. First look at what your water company reports for your postcode, because that is a laboratory value and therefore more accurate than any home test. If you want to measure yourself or record a change, take a drop test: every drop is 1 °dH, and that reads more precisely than a colour chart.

The figures to remember: 1 °dH is 17.8 milligrams of limescale per litre, the Dutch average sits at around 8 °dH, water companies may not soften below 5.6 °dH, and water is only called hard from 12 °dH upwards. That last threshold is the most important one, because the claim that 4 °dH is already hard comes from parties that sell softeners and is not correct.

And separate the two questions. Hardness is about minerals that are allowed to be there; a filter is about substances that do not belong there. If you come out at 14 °dH and the limescale bothers you, then you are looking for a softener. If you want to know what else is in your glass, that is a different conversation, and that is where our work begins.