The impacts of climate-related hazards are becoming a major concern for many people worldwide, especially those in vulnerable areas such as Puerto Rico. In September 2017, Hurricane Maria caused severe disruption to the island’s drinking water supply due to power outages, causing major problems for utility companies. This led to water insecurity, particularly among residents, who could not access safe, reliable, adequate, and affordable drinking water. Disaster-related water insecurity challenges are coupled with widespread public mistrust of tap water, yet some residents still consume tap water despite the mistrust. Alternatively, a portion of those who trust the tap water quality choose not to consume it. This knowledge–behavior gap needs to be explored to understand tap water consumption behaviors in the context of mistrust and insecurity. This study’s main goal was to identify why residents mistrusted their tap water and their behaviors in response to or despite mistrust. Data collection included household surveys and interviews with residents (n = 154) from May 2022 to July 2022. Thematic qualitative analysis shows residents generally mistrust tap water because of its poor quality over the past decade based on its palatability properties (taste, color, and smell). In addition, people trust or mistrust tap water because of their lived personal positive or negative experiences with the water utility service in Puerto Rico. This study can be used to develop strategies to address water insecurity and understand public trust in the tap water supply provided by water utilities. Ultimately, this research emphasizes the need for more studies to explore the knowledge–behavior gap in order to understand why some people consume tap water despite the mistrust and vice versa.