Hard water and coffee machines: a UK guide

Where water is hard in the UK

Water hardness depends on the rocks it passes through. Chalk and limestone areas give hard water, which covers much of London, the South East, East Anglia and parts of the Midlands and South West. Areas fed by upland rain and granite, such as much of Scotland, Wales, the Lake District and parts of northern England, tend to have soft water.

Hardness can vary between streets and change if your supplier switches source, so check your own postcode rather than relying on a regional map. Your water company publishes hardness figures online, usually through a postcode checker. The Drinking Water Inspectorate oversees water quality in England and Wales.

Reading your supplier's figure

Water companies report hardness in different units: milligrams per litre (mg/l) as calcium carbonate, Clark degrees, German degrees (°dH) or French degrees. Coffee machines usually ask for a level set from a test strip, often in °dH bands. Our water hardness converter turns any of these into the others.

As a rough guide, many suppliers band water something like the table below. Your supplier's bands may differ slightly.

Convert your water hardness →

Setting your machine's hardness level

Most bean-to-cup machines and many espresso machines come with a test strip and a hardness setting. The setting tells the machine how often to remind you to descale. Set it too soft and scale builds up before the reminder arrives.

1. 1

   Dip the test strip supplied with the machine in tap water for the time stated.

2. 2

   Count the coloured squares or compare with the chart on the pack.

3. 3

   Enter the matching level in the machine menu, as the manual shows.

4. 4

   If you fit a water filter, follow the manual, as some machines change the setting or reminders when a filter is active.

5. 5

   Recheck after moving house or if your supplier changes source.

Do water filters help?

Many makers sell a filter that sits in the water tank and reduces hardness and chlorine. In a hard water area, a filter means fewer descales and often better tasting coffee. Filters must be soaked or primed before use and replaced at the interval in the manual, often every couple of months or after a set volume. An expired filter does nothing useful.

A filter does not remove the need to descale, it just reduces how often. For model specific filter steps, see the Sage Barista Express water filter. Bottled water low in minerals can help in very hard areas, but avoid distilled or reverse osmosis water unless the maker approves it, as some machines rely on some minerals to sense water level and very soft water can taste flat.

Descaling: how often and with what

Descale when the machine prompts you, and more often if you notice slower flow, weaker steam or white flakes in the drip tray. Use the maker's descaler or one the manual approves. Most are based on lactic or citric acid. Many makers advise against vinegar, as explained in why descale a coffee machine and can you use vinegar.

For step by step routines, see how to descale the Sage Barista Express, how to descale a De'Longhi Magnifica and how to descale the Gaggia Classic. If you are choosing a machine for a hard water area, models with a built-in filter and clear descale reminders make life easier; see our best bean-to-cup coffee machines.

Note:Descalers are acids. Follow the label, keep them away from children and rinse the machine thoroughly afterwards as the manual describes.

Frequently asked questions

How do I know if my water is hard? Check your water company's postcode checker or use the test strip that came with your machine. White scale in your kettle is a strong hint.

What hardness setting should my coffee machine be on? The one that matches your test strip result. The manual explains how each strip result maps to a setting.

Should I use a water filter in a bean-to-cup machine? In a hard water area it usually helps, reducing scale and improving taste. Replace it on time and keep descaling when prompted.

Can I use bottled water in my coffee machine? Still bottled water with low mineral content can help in hard water areas. Avoid distilled water unless your manual says it is suitable.