compliant strategies

We have a project with an underground parking which covers the whole site. On top of that underground parking we have a 6 floor building and an open space with a green roof (on top of the underground parking structure) Question 1: If rainwater is captured and filtered through the green roof, can it then be discharged? Question 2: If we install a deposit, sized for the 95th percentile, would it be ok if, in case of a torrential rain event, that part of the water is discharged directly (without going to the tank) The project engineer is afraid the deposit would not be able to manage such an intense rainfall event and therefore suggests some way to discard the excessive rain. Question 3: If the water that is captured in the tank is then pumped to the green roof where it filters through the substrate and is then discarded from the site. Would that be compliant? Or does the water have to be used on the site (for toilets for instance)