The charity's Thirst For Change campaign urged the UK Government to raise issues of water poverty and sanitation at the meeting of the G8 nations at Camp David in the US last week.
Cafod's head of campaigns, Clare Lyons, said: "We are disappointed that the G8 seems to have overlooked one of the fundamentals of life - water, and that sanitation keeps being neglected."
Last week the charity delivered requests from more than 60, 000 Cafod supporters to 10 Downing Street urging the Government to ask other G8 nations to prioritise improving access to water and sanitation in their foreign aid budgets.