Direct electrochemical determination of arsenate (As V) in neutral pH waters is considered impossible due to electro-inactivity of As V. As III on the other hand is readily plated as As 0 on a gold electrode and quantified by anodic stripping voltammetry (ASV). We found that the reduction of As V to As III was mediated by elemental Mn on the electrode surface in a novel redox couple in which 2 electrons are exchanged causing the Mn to be oxidised to Mn II. Advantage is taken of this redox couple to enable for the first time the electrochemical determination of As V in natural waters of neutral pH including seawater by ASV using a manganese-coated gold microwire electrode. Thereto Mn is added to excess (∼1 μM Mn) to the water leading to a Mn coating during the deposition of As on the electrode at a deposition potential of −1.3 V. Deposition of As 0 from dissolved As V caused elemental Mn to be re-oxidised to Mn II in a 1:1 molar ratio providing evidence for the reaction mechanism. The deposited As V is subsequently quantified using an ASV scan. As III interferes and should be quantified separately at a more positive deposition potential of −0.9 V. Combined inorganic As is quantified after oxidation of As III to As V using hypochlorite. The microwire electrode was vibrated during the deposition step to improve the sensitivity. The detection limit was 0.2 nM As V using a deposition time of 180 s.