The present paper has focused on the potential application of multiwalled carbon nanotube for the development of a new, simple and highly selective electrochemical method for simultaneous Zn (II), Cd (II) and Pb (II) monitoring in water samples (lake and effluent waters). by using potentiometric stripping analysis (PSA). The electrochemical method is based on simultaneous preconcentration/reduction of metal ions onto a multiwall carbon nanotube electrode at -1.3 V (versus Ag/AgClsat) in 0.3 mol L-1 acetate solution containing 15 mg L-1 Hg (II) ions during 180 s, followed by subsequent chemical stripping. The analytical curve for all analytes covered the linear range varying from 58.4 up to 646.2 mu g L-1 with correlation coefficients higher than 0.981. The limits of detection for Zn (II), Cd (II) and Pb (II) were found to be 28.0, 8.4 and 6.6 mu g L-1, while the relative standard deviation (RSD) at 352 mu g L-1 was 5.6, 7.1 and 5.6% (n = 5), respectively. The behavior of the simultaneous determination in the presence of following ions Co (II), Cr (III) and Cu (II) was affected by using the analyte:interferent ratio 1:10. Therefore, by using standard addition method, Zn (II), Cd (II) and Pb (II) ions in lake and effluent water samples were determined after the spiking procedure and the results were successfully compared with those obtained by atomic absorption spectrometry (AAS). The obtained results suggest that the proposed method can be applied as a simple and efficient alternative for the simultaneous monitoring of heavy metals in water samples, according to those established requirements from environmental organizations. In addition, this method demonstrates the powerful application of carbon nanotubes in the field of potentiometric stripping analysis. (C) 2009 Elsevier B.V. All rights reserved.