<p>Accurate leak localization in water distribution networks (WDNs) remains a critical challenge. Acoustic methods have proven to be extremely popular in leak localization as they are purely sensor data-driven and have shown to work in a number of tests. However, the problem of optimal sensor placement (OSP) for acoustic leak sensors is yet unsolved for acoustic-based methods due to a lack of robust analytical or numerical methods governing the acoustic wave propagation in two-dimensional (2D) pipe networks. Existing OSP studies for 2D WDNs rely on pressure sensors and are supported by a hydraulic model, but not acoustic sensors, as the physics of acoustic wave propagation in 2D networks consisting of numerous discontinuities is not well understood, and empirical data to support acoustic-based models remain scarce or non-existent. To address this gap, we present a framework to solve the OSP problem utilizing acoustic sensors in a 2D WDN. The objective function is based on the concept of interior points, which are locations within the WDN where a leak can be pinpointed for given sensor placement locations. The optimization problem is solved using a Genetic Algorithm with a constraint based on sound attenuation, ensuring that leak signals are detectable at the optimally placed sensors. Additionally, a cost-benefit analysis is conducted to aid stakeholders in making informed decisions by optimizing the number of hydrants (cost) relative to the coverage area for pinpointing a leak (benefit).</p>