I agree with the others in ...

I agree with the others in that a maximum velocity for say 3 m/s should not be regarded as a standard but as a rough rule of thumb for pipe sizing. I can think of situations where 3 m/s would be acceptable and other where even 2 ft/s would be terribly high.

The goal is to provide adequate pressure for any reasonable situation. The basic question is "for what flow condition should you satisfy the max velocity target?" Is it max day, max hour, max day plus fire flow, average day with a parallel pipe out of service,...?