I used a little over 1 gallon in 4 20min. sessions on the road course at PIR.
By your description you would have used 2l. Granted my track time was 90% WOT, 5000 to 6500 rpm.
My nozzle is rated ~250cc/min static flow. My flow control is by injector duty cycle and maxes out ~85%. Injection triggers at 4psi boost.
In daily driving I use about 1 gallon of water for ~35 gallons of gas. (3 fill ups)
I have turned my injection pressure down about 40 psi so it varies between 90 - 110 psi max. It comes on at its lowest pressure early just as it starts to make boost at about 2500 rpm and then ramps up to max pressure. I have a 375 ml/min flow at 150 psi nozzle.
It still uses up the 2 L tank in about 10 min of playing.
I will have to be selective about using this system.
Now I see the down side of this technology. At least an air to water intercooler can be used longer without stopping for a refill.
Maybe next year I'll supplement it with a little bit of