Lead contamination of drinking water is a widespread problem affecting people in developing as well as developed countries. While lead contamination levels can be monitored at water treatment facilities, drinking water may get contaminated with lead during its distribution. To ensure that drinking water ‘at the tap’ is not lead contaminated, it is essential to develop a low-cost, portable sensor for use in homes and offices. In the present talk, a novel electrochemical sensor concept which enables accurate detection of ppb-levels of Pb²⁺ in water will be outlined. The sensor works on the principle of underpotential deposition of lead (Pb_upd) onto a Cu electrode followed by quantitative measurement of the hydrogen evolution reaction (HER) current on the partially Pb_upd-modified Cu electrode surface. The basic operation of the electrochemical sensor involves the following steps (Figure 1): (i) A copper working electrode is immersed in a Pb²⁺-contaminated sample, and a suitable electrode potential is applied to it which facilitates the underpotential deposition of lead onto the copper surface. Depending on the Pb_upd time and the Pb²⁺ concentration in the sample, the Pb_upd coverage of the Cu surface increases gradually; (ii) The kinetics of electrochemical splitting of water to evolve hydrogen gas depends on the Pb_upd coverage on the Cu electrode – higher the Pb coverage during step i, more sluggish is the hydrogen gas evolution during step ii. The degree of suppression of the HER kinetics (i.e., current) is measured, which then provides the Pb_upd coverage (for a known deposition time) and thus the Pb²⁺ concentration in solution. In this presentation, we will demonstrate the feasibility of the above electrochemical sensor concept to achieve a detection limit of 10 ppb Pb²⁺ in water samples. Furthermore, we will present detailed analysis of the sensor response time using a mathematical diffusion-reaction model. Techniques to minimize interference effects due to other contaminants, and comparison between the sensor performance and standardized spectroscopic measurements of lead concentration will also be discussed. Ongoing work on building a portable electrochemical sensor prototype will be outlined.