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Water, water filters and descaling

Oct 03, 2026

Water affects both the taste and how long your machine lasts. Limescale is the most common cause of expensive repairs, but water that is too soft or distilled is not good either.

The right hardness

Most manufacturers recommend 2–4 °dH (German degrees of hardness). Rocket, for example, specifies 2–4 °dH. Tap water varies a lot from region to region, often anywhere between 2 and 15 °dH. Measure it with a BWT water test or check the figures published by your local water supplier.

  • Below 2 °dH: the taste becomes flat and some machines cannot detect the water level. Do not use distilled water.
  • 2–4 °dH: perfect. A simple in-tank filter for taste is enough.
  • Above 5 °dH: use a filter that reduces hardness, or a plumbed-in connection with BWT Bestmax.

Filters in the water tank

A water filter for the tank attaches to the hose in the tank and removes chlorine and some of the limescale. Replace it every 2–3 months. Sage machines use Claris filters; see the relevant model page.

Plumbed-in connection

Machines with a rotary pump can often be connected directly to the mains water supply. In that case we always recommend a BWT Bestmax filter. Read Plumbed-in connection and BWT Bestmax.

Should I descale?

  • Thermoblock, single boiler and Sage: yes, as described in the manual, usually every 1–3 months. Use Cafetto LOD descaler.
  • Heat exchanger and dual boiler (for example E61 machines): no, prevent limescale instead with the right water and a filter. Many manufacturers advise against descaling yourself. Rocket states that it does not recommend descaling because the descaler can cause corrosion and is hard to rinse out completely; contact an authorised workshop if the boiler needs descaling.

Changing the boiler water

Water that sits in the boiler for a long time tastes worse. Rocket recommends changing the boiler water at least once a month, every other week with heavy use. The easiest way on a heat exchanger machine: draw off 1–2 litres of hot water through the hot water valve (or steam valve) while the machine is hot and the pump refills it with fresh water. Follow the manual for your model.

Not sure what applies to your machine? Contact us with your model and water hardness and we will help you choose the right filter.

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