Water hardness describes the amount of naturally occurring dissolved minerals in your water, primarily calcium and magnesium. Water containing higher concentrations of these minerals is described as hard water, while water containing lower concentrations is considered soft water. For coffee machines, hardness matters because these minerals can form limescale as water is repeatedly heated.

Every time your coffee machine heats water, scale-forming minerals can gradually leave deposits inside the heating and hydraulic systems. The harder the incoming water, the greater the potential for limescale accumulation. Knowing your water hardness helps you manage descaling, water filtration and any water-hardness setting provided by your machine.

You can test your water using a water-hardness test strip, which changes colour according to the mineral content of the water. Your local water supplier may also publish water-hardness information for your area. Testing the water actually being used in the machine is particularly useful if you use a household water treatment or filtration system.

The water-hardness setting helps the machine account for the quality of the water being used. On machines that calculate maintenance requirements, the setting can influence when a descaling reminder is displayed. Setting the machine for water that is significantly softer than the water you actually use could result in descaling being requested less frequently than appropriate.

Generally, harder water creates greater potential for limescale formation, so maintenance may be required more frequently. However, there isn't one descaling interval suitable for every owner. Water hardness, machine usage, filtration and the volume of water passing through the machine all influence how quickly scale can accumulate. Follow your machine's maintenance system and respond to changes such as reduced water flow where appropriate.

If your coffee machine is designed to accept a compatible water filter, using one can help reduce the amount of scale-forming minerals entering the machine. This can be particularly useful in harder-water areas. The filter still needs to be correctly prepared and replaced when required, and it shouldn't automatically be treated as a permanent substitute for descaling.