The rated capacity of the filters is generally based on chlorine removal under NSF certification or testing however many of our filters have been de-rated or the capacity reduced to allow for different conditions around the country. The 4000 litre capacity of the K9 & K10 filters is based on chlorine and needs to be reduced to 1800 litres for Chloramine, higher than a normal GAC due to the cartridge design and KDF media.