The function MKRIoTCarrier_Relay::close() sets the relay output pin LOW. The function MKRIoTCarrier_Relay::open() sets the relay output pin HIGH.
MKRIoTCarrier_Relay::begin() calls close() so it sets the output pin LOW and turns the water pump OFF.
Whatever is causing the water pump to turn ON (carrier.Relay1.open()), it is NOT the library.
Also, shortly after you call carrier.begin(); in setup() you also call carrier.Relay1.close(); which would turn off the water pump EVEN IF carrier.begin() had turned it on.
There must be a mistake elsewhere in your sketch that is turning the water pump on when you don't want it to be on. Check your program logic.