The aim of this study was to investigate the effect of sound insulation on the usage water piping in multi-storey apartment buildings constructed using a reinforced concrete shear wall structural system. Indoor noise levels in two apartments, one located below the other, were measured. The water piping in one of the apartment buildings was constructed using sound insulation, whereas the other was not. Noise sources were created in a bathroom of one apartment and measurements, according to EN ISO 3822-1, were made in the adjoining bedrooms, above and below. The findings of this study show that the equivalent sound level measured in the main bedroom of the apartment in the insulated building just below the one in whose bathroom the source of noise had been created was 2.9 dBA below the maximum noise level recommended by the NR criterion. In contrast, the equivalent sound level measured in the same location of the uninsulated building was 4.3 dBA above the maximum noise level recommended by the NR criterion. (C) 2005 Elsevier Ltd. All rights reserved.