Will this tank meaningfully balance roof yield and non-potable demand?
One millimetre over one square metre is one gross litre before losses. Apply the entered Hong Kong runoff and retained-system factors, then compare the tank with demand and reserve days; annual yield alone is not a storage guarantee.
Method
Gross yield is area times rainfall. Retained yield applies runoff and system efficiency; captured water is bounded by tank capacity, while overflow and reserve shortfall remain explicit.
Important limitation
This is for non-potable planning only. It cannot prove water quality, treatment, backflow protection, structural loading, drainage approval, storm attenuation or actual rainfall distribution.