Filter cartridges are an essential feature of a Lay-Z-Spa pump as they filter out dirt and grime from the water in the hot tub to help keep it clean and healthy. They also prevent dirt from getting into the pump and heater which could cause damage and reduce its lifespan. Filter cartridges work by catching dirt and grime when the water is pumped through them. As your pump will usually be continuously cleaning and filtering the water when it is turned on, dirt can quickly build up, especially when the hot tub is regularly used.