A sensor for the determination of orthophosphate (PO43-) concentration in water was developed that utilizes the enzymatic cleavage of maltose in the presence of PO43- to generate an equivalent amount of glucose. The glucose produced from this reaction was quantified using a commercial glucometer test strip coupled to a miniature potentiostat using amperometry. This sensing approach yielded a limit of detection of 1.45 μM (0.1 ppm) glucose/PO43-, which is lower than that of a commercial glucometer (≥600 μM glucose), and a dynamic range of 10 μM-3 mM. The selectivity of the approach to PO43- was evaluated by determining the device's response to known components in natural water samples. Finally, we showed that the approach can be used to determine PO43- in tap and river water samples.