The physics
Water does not squeeze into less space. So the same volume passes every part of a pipe each second. Where the pipe is narrow, the water moves faster.
A₁v₁ = A₂v₂
In steady, streamline flow, the dye lines never cross. Along a streamline, pressure and speed trade. Fast water has low pressure.
P + ½ρv² + ρgh = the same all along a streamline
An open gauge tube shows the pressure as a column of water, P = ρgh. A venturimeter uses the gap between two gauges to find the flow.
The same rule explains a sprayer, a wing's lift and a chimney's draught. Fast air over a tube top, or over a wing, has low pressure.
lift = ½ρ(vtop² − vbelow²) × A
Bernoulli's rule needs a steady flow. For a train in a tunnel, ride with the train. Then the air flows steadily past it.