From a plumbing code perspective, there are no requirements.
I have attached the information I have used for guidance for gallons per day usage per person in different types of buildings. It is based on information provided by AWWA.
usage and storage requirements are not the same. there are a number of other factors that would influence the amount of storage you want. primary ones are fire, emergency and to handle peak flow times where your water production source cannot provide a high enough flow rate