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.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.