The oxygenics, a popular replacement head, claims a max of 2.5 gals per minute which is supposed to be a savings so maybe 2.5 to 3 gals per minute. If you are trying to calculate how long it will last I can tell you we took two 3 to 5 minute showers this winter back to back without running out of hot water. I would not have gone for three though. Also you can speed recovery time by turning both gas and electric on.
2005 Wolf Pack WP22-2016 Grey Wolf 26RR-Gone
2004 Siverado 2500HD Duramax
2013 Keystone Springdale 5r
1998 Honda Valkerie
2016 Camping 148 days so far