Is the father living on the second floor obligated to share in the costs of the shared water pump, even though water reaches him without needing it, and would he be sinful if he doesn't?

If a person does not benefit from the water, he is not obligated to share in its costs. As for the additional cost resulting from operating the motor, he must share in it if he benefits from it, otherwise he is not obligated to pay. Nevertheless, it is recommended to participate in bearing the costs of operating the device even if he does not benefit from it, unless it causes him great hardship.