The agency is looking to secure corporate sponsorship for fresh2o, a specially comissioned series of photos of celebrities being used to promote the charity.
It has been hired by fashion photographer Candice, who has taken underwater pictures of stars such as Keira Knightley, dressed in a Jenny Packham gown.
Other celebs who have taken part include Lily Cole, Kelly Brook and footballer Eider Gudjohnson. Candice chose One after approaching four agencies.
Fresh2o, designed to raise international awareness of WaterAid's work in developing third world access to drinking water and sanitation, was launched last year but has not had PR support before.
Account manager Katherine Acton said: ‘It will be an image-led media relations campaign. By getting sponsorship, we hope to disseminate the images for free.'