In many coffee machines, yes. A water filter is often optional rather than essential for operation, although this varies by machine. If you remove the filter, make sure the machine's filter setting is updated where applicable and check the instructions for your particular model. Without filtration, limescale management becomes particularly important.

Without a filter, untreated water passes directly into the machine. Depending on your local water quality and hardness, this can result in faster limescale accumulation within the heater and internal water circuit. It may also affect the taste of the water used to prepare your coffee.

Potentially, yes. A suitable water filter can reduce the amount of scale-forming minerals entering the machine. Without one, limescale may accumulate more quickly, particularly in hard-water areas. Make sure the machine's water-hardness setting is correct and descale when required.

Yes, where your machine has a filter setting or filter-monitoring function. Leaving the machine configured as though a filter is installed could affect its maintenance reminders. Deactivate or reset the filter setting according to your machine's instructions and make sure the correct water-hardness level is selected.

Not necessarily. Bottled and externally filtered waters can have very different mineral compositions, and not every type is ideal for a coffee machine. Very hard water can increase scale formation, while water with very low mineral content can also affect coffee extraction and machine operation. Use water suitable for your particular machine rather than assuming any bottled or filtered water is automatically better.

If your machine is designed to accept a water filter, using the correct filter can be beneficial for reducing limescale and maintaining water quality. How valuable it is depends on your water hardness, machine usage and maintenance routine. A filter isn't a substitute for good machine care—it is another way of helping manage the water entering the machine.