Why does your housing society pump consume less and less current after running - Its rating is 9 Amp it starts with 6.4 reducing slowly to 5 Amp?

All electric motors have a inrush of current at startup in excess of what it takes to continue running. There are a number of reasons for this some of them requiring an in depth knowledge of physics and electricity.

But a simplified answer is it takes more energy to get an object started into motion from being at rest... than to maintain that motion once started.

Smoothys simple explanation is also a simple explanation of Newton's First Law. Because of inertia it takes more energy to get started than to keep running.

Agree with the previous explanations plus the fact that the start windings of the motor as well as the run windings are energized during start up. After reaching approximately 75% of run speed, the start windings are de-energised.