This article reviews the relationship between salmonid aquaculture, both in fresh and saltwater, and water quality, focusing on the effects of bad water quality at the lethal and sublethal level, water quality assessment using physicochemical parameters, and new developments for water quality estimations: from mathematical indices and models for the interpretation and/or prediction of analytical results, to the assessment of water quality by biological methodologies. The main problems of different rearing systems, for example, land‐based farms and caged and net‐pen salmonid cultures, are also considered, taking into account not only the water quality problems originated by the culture conditions but also those related to external causes of water pollution.