Good static pressure does not prove delivered flow

A fictional building has satisfactory pressure at its incoming gauge while all outlets are closed. During simultaneous use, an upper-floor outlet delivers much less flow than expected. The actual route includes a partly obstructed fitting, long piping and a pressure-control device whose setting has not been verified. A contractor concludes that replacing every pipe with a larger diameter is the only possible answer. The exercise supplies no mandatory Swiss pressure or velocity limit and performs no work on the water supply. Explain why static and flowing evidence must be distinguished and how actual height, losses, demand and credible measurements guide an accountable investigation before selecting a physical change.