This work reports the fabrication of portable system for the determination of trace As(III) in water samples by mean of anodic stripping voltammetry (ASV). The portable detection system consists of a three-electrode mini cell featuring injection-moulded plastic conductive electrodes. As(III) accumulates on the disposable working electrode by electrolysis forming in situ an alloy with co-deposited gold. Then, the accumulated arsenic is detected by applying an anodic potential scan on the working electrode. The chemical and instrumental conditions were studied and the analytical parameters for the determination of As(III) were established. The limit of detection was 0.2 μg L-1 and the repeatability at the 5.0 μg L-1 As(III) level (n = 10) was 4.7 %. The portable set-up was applied to different groundwater samples with recoveries between 95 and 105 %.