The business was previously with Starcom but the Publicis network withdrew last year from a wider global buying review casting doubt on its UK relationship with Danone.
Planning for the Evian, Volvic and Badoit brands will switch to Carat over the next month.
Last June, Carat won the UK planning task for Danone's dairy division, which was previously with Mediaedge:cia. It handles UK buying for Danone but this business is being reviewed as part of the global buying review process.
Danone is holding the £300m buying review to cut its roster of agencies and to improve its purchasing power.
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