Following a request from the European Commission, the Panel on Additives and Products or Substances used in Animal Feed (FEEDAP) was asked to deliver a scientific opinion on the efficacy of guanidinoacetic acid (GAA; Creamino®), intended for use as zootechnical additive (functional group: other zootechnicals – improvement of performance parameters) for weaned piglets and pigs for fattening in water for drinking. The additive is already authorised for use in feed and water for chickens for fattening and chickens reared for laying/breeding and only for feed in weaned piglets and pigs for fattening. In the previous opinion, the Panel concluded that the additive is safe for chickens for fattening, chickens reared for laying/breeding, piglets and pigs for fattening, the consumer, users and the environment under the proposed conditions of use. In the current submission, the applicant submitted considerations to support the authorisation of GAA in water for drinking for weaned piglets and pigs for fattening. The FEEDAP Panel reiterates it previous conclusion that the use of GAA in feed and water for drinking of weaned piglets and pigs for fattening has the potential to be efficacious in improving the zootechnical performance of the target animals under the proposed conditions of use (600–1200 mg GAA/kg complete feed; 200–600 mg GAA/L water).