Why the pressure decrease when water flowing through a broader pipe enters a narrow pipe?

When water flows from a broader pipe into a narrow pipe, its velocity increases due to the principle of continuity, which states that the flow rate must remain constant. As the water speeds up in the narrower section, the pressure decreases according to Bernoulli's principle, which relates the speed of a fluid to its pressure. This pressure drop occurs because the energy of the fluid is conserved; the increase in kinetic energy (due to higher velocity) comes at the expense of potential energy (pressure). Thus, as fluid enters the narrower section, the pressure must decrease.