Background: Peru is one of the countries with the lowest percentage of population with access to safe drinking water in the Latin American region. This study aimed to describe and estimate, according to city size, socioeconomic inequalities in access to safe drinking water in Peruvian households from 2008 to 2018. Methods: Secondary analysis of cross-sectional data using data from the 2008–2018 ENAHO survey. Access to safe drinking water, determined based on the presence of chlorinated water supplied by the public network, as well as socioeconomic variables were analyzed. A trend analysis from 2008 to 2018, and comparisons between 2008 versus 2018 were performed to understand and describe changes in access to safe drinking water, according to city size. Concentration curves and Erreygers concentration index (ECI) were estimated to measure inequalities in access to safe drinking water. Results: In 2008, 47% of Peruvian households had access to safe drinking water, increasing to 52% by 2018 (p for trend < 0.001). For small cities, access to safe drinking water did not show changes between 2018 and 2008 (difference in proportions − 0.2 percentage points, p = 0.741); however, there was an increase in access to safe drinking water in medium (difference in proportions 3.3 percentage points, p < 0.001) and large cities (difference in proportions 12.8 percentage points, p < 0.001). The poorest households showed a decreasing trend in access to safe drinking water, while the wealthiest households showed an increasing trend. In small cities, socioeconomic inequalities showed an increase between 2008 and 2018 (ECI 0.045 and 0.140, p < 0.001), while in larger cities, socioeconomic inequality reduced in the same period (ECI: 0.087 and 0.018, p = 0.036). Conclusions: We report a widening gap in the access to safe drinking water between the wealthiest and the poorest households over the study period. Progress in access to safe drinking water has not been equally distributed throughout the Peruvian population. Promoting and supporting effective implementation of policies and strategies to safe drinking water, including equity-oriented infrastructure development and resource allocation for most vulnerable settings, including emerging small cities, is a priority.