I don't know what my shower flow is with my Oxygenics. But I take short showers anyhow. I spent years on boats and in the Caribbean where water is so precious and we use so little.
What I like about the Oxygenics, is the pressure is stepped up so that I can rinse off quickly with good water pressure from the shower whether I am on 12 volt pump or street water. Also, I don't wash my hair everyday, it's not at all necesarry if you keep it brushed often. Brushing often moves the natural oils from your head to the rest of the hair. So I can take a shower with very little water when I am not washing long hair *giggle*.
But I do like the nice stepped-up presure from the Oxygenics.
How to save water and get clean, if you are overly worried about filling up your gray water tank:
For a water-saving shower, soak your clean wash cloth in the sink. Add liquid soap. Get in the shower, and scrub down with the washcloth. Start with your cleanest parts and work towards the dirtiest parts of your body. This is so you don't wash the armpits first and then put that stinky on your face (besides, you could hurt your head this way when you pass out and fall down!)
Anyhow, now you just rinse off all the soap and dirt and scum (just how dirty do you get each day?) by making use of the handheld shower. You don't need to stand there for 10 minutes with the water spraying over you like you're at home with endless time and water. You can riinse off pretty quickly.
I spent 5 or 6 months living in my RV saving up money to repair the hot water heater, so I can also recomend that cold showers are a great way to save on water too!
I now have hot water, but I only need to turn it on once or twice a day for a few minutes. The insulation in the tank is incredible, or else it is set to near boiling. I turn it on when I am taking a shower or washing dishes, then turn it back off when I am done. I haven't run out of super hot water yet.
Besides saving on the shower holding tank, my poop holding tank goes a lot further because I never ever put toilet paper in it. I put all that in the garbage bag in the bathroom.
Since I use the same identical small plastic grocery bags for all my garbage in the kitchen and the floater can, I typically dump my small garbage daily anyhow. The grocery stores seem to provide me enough bags with the groceries to handle all my garbage and then some. It means you can use all the toilet paper you need to, just don't put it down the toilet, throw it away in hthe garbage instead.