I use autopots. The system is considered hydro. The medium is 50/50 coco/perlite. I use a 12 gallon rez, measure nutrients in liters, and I've noticed that at the height of the stretch four plants will take up about 15-20 liters every 2-3 days or a little more often, they slow down after the stretch and stay steady the rest of the way. At the end they are taking up about 10 liters every 3-4 days. I don't flush the plants and keep the nutrient solution set at 1ML per L to the very end. I flushed a grow once, but only once. I stopped checking the root-ball after every grow because they all look the same, healthy. The only time they didn't is a grow I did using a Gas Light grow schedule. The roots didn't develop.
Would plant training enter into the equation? I top my plants and sometimes lollipop, mostly don't. Would a plant that had more foliage on it consume more than one that didn't? I'm thinking mainline. If I understand it the mainline forces the plant to focus only on the 8 or 16 buds created by the mainline. Would that make it take up more water, less, or does it matter? And would a hybrid that grows short and wide consume as much as a sativa dominant plant that grows tall?