Water-Jet Weaving
Pressure buys velocity as a square root, so doubling the speed of insertion costs four times the pressure. Wide water-jet looms are expensive for exactly that reason.
— m/s
At the nozzle exit for the working pump pressure
The coupling ratio is the whole uncertainty here — it depends on yarn type, shed geometry and how far down the shed you measure, and it is not constant across the width. Water-jet weaving suits hydrophobic filament yarns; the water leaving the loom carries size and finish and belongs in the effluent balance.
Water-Jet Loom Pump Pressure & Weft Insertion Calculator — free, with the formula and a worked example, at Textile School.