2000 Fiesta 1.8 TD Van - Water leak

[Origin Unknown]

Assuming it's the water pump that given up after removing as many of the covers as possible to take a look. CBA to do it myself so taking over to a mechanic friends and it can sit on his drive until he has time. Quick question, filled up with water, can I leave the lid loose so that it won't pressurise? It's leaking heavy.