Highlights  Film shaped sensory polymeric materials change their color in presence of phenols  The polymers main chains have pendant diazonium moieties  The sensory materials are manageable and stable along time  The detection is achieved visually and also using pictures taken with smartphones  The limits of detection were of the order of ppb Abstract We have prepared polymeric films as easy-to-handle sensory materials for the colorimetric detection and quantification of phenol derivatives (phenols) in water. Phenols in water resources result from their presence in pesticides and fungicides, among other goods, and are harmful ecotoxins. Colorless polymeric films with pendant diazonium groups attached to the acrylic polymer structure were designed and harmful phenols water media