switching device for motor
You should use a contactor or motor starter that is rated in horsepower. Devices rated in horsepower are specifically designed for use with motors considering the brief surge of high current that occurs when the motor is switched on and accelerated to full speed. The design also considers the need to interrupt the high current that would occur in the event that the motor becomes stalled. Even some relatively small relays are sold with motor horsepower ratings. Purchase a contactor or relay based on motor horsepower and voltage ratings, not motor current.

A motor starter is a motor contactor with an overload relay sold as a single device. A combination starter also includes a fused disconnect switch or circuit breaker to provide ground-fault and short-circuit protection.

There is not much difference between a motor contactor and a relay that has a motor power rating. For a given power rating, the contactor can be expected to have a longer service life and a better tolerance for frequent on/off operation. Relays rated for motor use are likely to be available only for small motors. A contactor may be the only option for a 2 Hp motor. For automatic switching of a water tank pump motor the on/off switching could be quite frequent. It is probably not the best idea to buy the least expensive switching device that you can find. Unless the motor has built-in overload or over-temperature protection, external overload current protection should be provided.

8 amps is quite a low current for a 2 Hp, 230 volt, single-phase induction motor. For 8 amps, the efficiency multiplied by the power factor be 0.81. I believe that "class E" may indicate a high efficiency design. If that is the case, it is probably a better than average quality motor.