The size of a nozzle opening is roughly the thickness of a human hair, and that can easily be clogged with a grain of sand or a granule of rust, that is why it is essential that the nozzles are protected with a 5 Micron sediment Filter.

If the water is hard, then a Polyphosphate filter is needed to prevent or reduce, (depending on how hard the water is) lime build up and clogging the nozzles due to calcium present in hard water.

Polyphosphate: the filtering media, treats the hardness of the water by changing the molecular structure of Calcium. Here is how it works in layman terms: When you look at Calcium under the microscope you will notice it has claw shape crystals, those claws are the building blocks of lime and scale and are the cause of lime buildup (after misting with regular tap water). What the Polyphosphate does is that it removes those claws, and by declawing the Calcium it becomes smooth, more like pebble surface, and that is why although the Calcium is still present in the water, yet it had changed its structure and runs smoothly through the nozzles and does not accumulate to clog them.