Consider this...
Dinner has just been prepared and you want to get an additional glass of water. The Storage Vessel was emptied to prepare the meal. Let's assume it's a 24 GPD* Reverse Osmosis system. In approximately 1 hour, it will produce another gallon of pure water. It would take 3.75 minutes to produce an 8 oz. glass of water.A smaller system, a 5 GPD* system, would produce 26 oz. per hour. You could tap an additional glass in 18.5 minutes and the system would again be depleted.
When considering the capacity of a Reverse Osmosis system, recovery time is more important than the total water production per day.