Arduino Uno rev 3 toggling a 230 V submersible pump on intervals
The Arduino will easily drive this relay board, and it needs only a very small input current.

The board you linked to has a built-in optical isolation circuit, so there is no direct electrical connection between the Arduino-side of the circuit and the relay side. This should protect your Arduino if something goes wrong. For what it's worth, the product description specifies this board is suitable for "AC [...] appliances such as [...] motors". A pump is primarily a motor.

The voltage may fluctuate when the pump is started and stopped (Back-EMF). It's hard to say what this might do to the relay board if it goes way over specification. Perhaps you might be happier with a much more robust solid-state relay (SSR) that has a higher rating than the target load. Something 
like SSR-25DA 25A Solid State Relay - White. Since solid-state relays are non-mechanical, they will not wear-out from repeated switching either.

You may also want to build some fail-safe sensors into your project. For example, water level float switches for both high-water and low-water marks.