How to test water hardness for a coffee machine

Coffee-machine hardness settings are often selected during first setup, when most of us want to make a drink rather than interpret water chemistry. A wrong setting can make maintenance prompts poorly aligned with the water actually used. You do not need a laboratory for a useful home result, but you do need the right test and units.

Start with your UK water supplier

Use Water UK's postcode supplier finder, then locate the supplier's water-quality or hardness lookup for your address. Record the result, unit and date. Some companies report milligrams per litre as calcium carbonate (mg/L CaCO₃); others show degrees or a category. A postcode result reflects a supply zone and can change, so it is a baseline rather than an immutable reading at your particular tap.

If your machine includes a test strip, use that first for its setup scale. If not, obtain a suitable drinking-water hardness test with a clear colour chart and instructions. Do not use a pool strip's unrelated “total alkalinity” square as if it were the machine's total-hardness reading.

Test the actual filling water

1. Run the cold drinking-water tap briefly according to your supplier's normal water-quality guidance. Use a clean glass, not a cup coated with coffee residue.
2. Dip the strip only for its stated time, remove it as directed, and wait the specified reading interval. Do not compare it immediately if the leaflet says the colour develops.
3. Compare the correct pads with the included chart in good daylight. If the colour sits between bands, repeat with a fresh strip rather than inventing decimal precision.
4. Write down the result and its units. Convert only using the machine manual or test maker's table; do not enter a bare “10” from one scale into another.
5. Set the machine to the corresponding level, then record whether an in-tank filter is installed. Follow the model's reset procedure if you later change water source.

Test the water after a jug filter if that is what you put in the tank; the supply report describes water before the home cartridge. If the home uses a salt-regenerated softener, first confirm whether the kitchen tap bypasses it. Our softened-water guide explains why that distinction matters.

Why TDS is not enough

A TDS pen measures conductivity and estimates total dissolved material. It cannot distinguish calcium and magnesium hardness from sodium or other dissolved ions. Two waters with similar TDS may have different scale behaviour. TDS can be useful for a different question, but it is not a substitute for the hardness strip or model-specified water test. Our broader UK water-hardness guide expands the distinction.

When to retest

Retest after moving, changing supplier, installing or removing a filter, bypassing a softener or seeing a surprising mismatch between a recent result and machine behaviour. A single rapid descale alert does not prove the strip is wrong: first check whether the previous cycle finished, the filter option was set correctly and the machine was reset as the manual requires.

Frequently asked questions

Can I use a postcode result instead of a strip?

Often it is a reasonable starting category, especially for a simple brewer. Use a strip when the machine specifies one or when home treatment may change the water between supplier and tank.

Is white scale in my kettle a test?

It suggests scale formation over time, but does not give a measured hardness level. Use a supplier result or proper strip to set a machine.

What if my strip gives a different value from the supplier?

Check units, strip age, read timing, tap source and any home filter or softener. Repeat the test, then contact the supplier or machine maker if the discrepancy affects a model setting.