In their first appearance at the worlds in a decade, where they fell to a 14-1 loss against Canada in 2003 also in Barcelona, Britain took a 5-4 lead just before half-time.
However, the Canadians responded and went into the interval 7-5 ahead and never relinquished their stranglehold on the tie in the Catalonian capital.
Next up in the group for Britain is a clash against reigning world champions Greece on Tuesday quickly followed by Olympic gold medallists USA on Thursday.
After those encounters all eyes will then turn to the knock-out competition on Saturday, but 26-year-old left winger Chloe Wilcox claims there are plenty of positives to build on.
"It was a hard game but we stayed in it and we had some moments in the game where we got back to within one goal," said Wilcox.
"But then we let our concentration slip again for two minutes and that type of team punish you for that, for those easy mistakes.
"But it's promising; we've played some really good water polo so we can only get better."