Time Domain Reflectometry (TDR) is a technique employed in the detection and localization of water leaks, particularly in district heating networks. In this method, a 2-wire sensor is utilized along a twin-pipe insulated with low electrical permittivity materials $(\varepsilon_{\mathrm{r}}\approx 1)$ to form a transmission line (TL). A leak saturates the insulation with moisture, causing a distinct decrease in the characteristic impedance $(\mathrm{Z}_{0})$ of the TL, thereby a change in the reflected signal. The temporal difference between the transmitted and reflected signals (time of flight (ToF)) is an indicator of the leak's distance. Due to the fast propagation of electromagnetic waves, conventional TDR devices require high-speed ADC, resulting in bulky, power-hungry, and costly instruments [1]. Bypassing high-speed ADCs as an alternative approach requires substantial digital infrastructure [2], [3]. Due to these limitations, it is not feasible to use TDR systems in battery-less Wireless Sensor networks (WSN) powered simply by temperature gradients between hot and cold pipes in a twin-pipe setup. For this application, with an acceptable precision of 0.5m, a simpler and cost-effective implementation is required. This paper presents an energy-efficient TDR front-end fabricated in a 65nm CMOS that can be used in a WSN. The system block diagram is shown in Fig. 1. The sensor is activated to collect data, which is then time-stamped by a host MCU, and transmitted wirelessly to a hub/drone. In this system, energy is harvested by a thermoelectric module connected between hot and cold pipes and stored in a 1F supercapacitor. The TDR front-end achieves a remarkable 0.14m accuracy while drawing only 3mA from a 2.5V supply, offering a faster and more cost-effective solution for smart continuous monitoring of district heating networks.