How much does a hydrogrown plant drink per day?

Going to build a flood/drain system and need advice on reservoir size..the grow table will hold 12 girls, veg to 12-14 inches. I know there is a lot of variables to consider but generallly, how much does a plant drink per day in full bloom? Will use 2x600w hps.

Thanks

My rule of thumb is to have 5 gallons of water in the reservoir per decent sized plant in the system so the water stays stable and don't need to top off every day or so.

I've used to grow 22 plants in a recirculated dwc system with a 15 gal res and the ph keep bouncing up every hour.