Yes, be VERY careful with the 230V volt part of this. Put the relay near the pump, and run only a signal circuit to Arduino. An opto-isolated relay or "Solid State Relay" would be best.
This is overkill with number of relays, but they are optically isolated: (DISCLAIMER: From my shop, but there are other suppliers too):
http://arduino-direct.com/sunshop/index.php?l=product_detail&p=156