The challenge of providing sustainable and safe water services in regions lacking centralized water infrastructure can be addressed through the utilization of on-site treatment and reuse of wastewater. However, the widespread implementation of decentralized water reuse systems is currently hindered by the considerable expenses associated with remote water quality monitoring. Specifically, when using chlorination for treatment, the fabrication and maintenance costs of free chlorine sensors pose significant drawbacks to their implementation. In this letter, we present an alternative solution by mitigating the sensor cost through the utilization of electrochemical sensing coupled with a cleanroom-free sensor fabrication process. We meticulously optimized the electrodeposition process to enhance sensor stability and ensure reproducibility, achieved through precise control of reactant concentrations. Our findings demonstrate the feasibility of obtaining consistent measurements in treated graywater by employing controlled Prussian Blue electrodeposition on readily available screen-printed electrodes, resulting in variation as low as 7.44% (n = 6). Furthermore, cyclic voltammetry experiments reveal a distinct peak at -0.11 V, indicating the presence of free chlorine in treated graywater samples. This characteristic is leveraged in chronoamperometric sensing, enabling robust chemical detection with a wide dynamic linearity range (R^2 = 0.9933) spanning from 0.06 to 6.28 ppm of free chlorine in treated graywater samples and a competitive sensitivity reaching 7.6 μA/cm^2 per ppm.