In a word, wrong. Yes, we have debated this to death, but that does not mean that everyone reached a consensus.
The referenced post makes at least two incorrect assumptions. One, that the maximum power consumed by the motor occurs at a mythical point of both maximum flow and maximum head. These two conditions are mutually exclusive of one another. The second is that the "flow energy" or whatever they heck they called it, is the only energy put into the fluid.
You've got motor inefficiency and pump inefficiency. For all practical purposes, all of the pump inefficiency goes into the water. Whether or not the motor inefficiency goes into the water depends on the particular situation. Submerged? No question it all goes into the water. Open-air? Most will convect off the motor casing into air with very little going into water.
A "typical" motor, however, will operate at >75% efficiency. Not so the typical pump. These tend to max out around 50% (among the pumps we use) or less. The "lost energy" is due to churning of the water that doesn't produce flow. It's the eddies and shearing around the impeller and between the impeller and volute.
If someone wanted to be really geeky about this, all you need to do is measure torque on the impeller shaft. Torque times rpm equals input power to the water. The fact that only a portion of this power is useful, namely flow rate times pressure rise, is irrelevant. The power still goes into the water.
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