The hydraulic power is what the water receives. The shaft power is what the motor has to hand the pump to make that happen, and it is always the larger of the two, because impellers leak, recirculate, rub and stir. The gap between them is the pump efficiency.

$\eta = \dfrac{P_{hyd}}{P_{shaft}}$ — read aloud eta equals P-hyd over P-shaft, with $\eta$ the Greek letter eta. $P_{hyd}$ is the hydraulic power delivered to the liquid, in kilowatts; $P_{shaft}$ is the mechanical power absorbed at the coupling, also in kilowatts; and $\eta$ is a bare ratio between 0 and 1 — quoting it as a percentage is a courtesy, not a unit. Turned round for the number you usually want, $P_{shaft} = \dfrac{P_{hyd}}{\eta}$.

Say the direction out loud once and you will never invert it: efficiency divides on the way from water to shaft. If your shaft power comes out smaller than the hydraulic power, you multiplied, and you have just described a pump that generates electricity. An efficiency above 100 % is the same error wearing a different hat — it is arithmetic, not a discovery.

Then the last step is a purchasing decision rather than a calculation. Motors come in standard frames — 5.5, 7.5, 11, 15, 18.5, 22, 30, 37, 45, 55 kW — and you buy the first one ABOVE the shaft demand, never the nearest. Nearest-but-under is a motor that runs on its service factor for a season and trips on the hottest afternoon of the year. Nor is oversizing free: a motor loafing at a third of its rating drags its power factor down and takes the cable and breaker up with it.