How much mass of water are we talking about here in these leaks? From
http://www.airbus.com/fileadmin/medi...80-Dec2014.pdf
Capacity: (1) Total Capacity - Standard configuration (six tanks): 1700 l (449 US gal)
Optional configuration (seven tanks): 1998 l (528 US gal)
Optional configuration (eight tanks): 2267 l (599 US gal).
Given that the flight was only 90 minutes from Heathrow, a large proportion of the potable water would already be in the passengers and waste tanks.
If the galley with the leak was one that can be moved fore and aft to suit the seating configuration, and was at the limit of its travel, it may be that the pipe was difficult to attach to the floor connection and not seated properly even before the attack from the trolley.