Although the H2Flow is capable of serving up to 10 gallons per minute water flow, the ideal maximum flow rate that can be run through the H2Flow for most effectiveness is 6 gallons per minute. The H2Flow cartridge should be replaced every 2 years.
See spec sheet and installation manual for more detail located at: http://support.noritz.com/technical-literature.php
Flow Rate
measure of fluid volume (e.g. water, gas) per unit time