OBJECTIVE: On November 20, 2021, petroleum fuel contaminated the Red Hill well, which provides water to about 93 000 persons on Oahu, Hawaii. Initial investigations recommended further evaluations of long-term health effects of petroleum exposure in drinking water. We reviewed electronic health records of those potentially exposed to contaminated water to understand prevalence of conditions and symptoms. METHODS: A sample of persons potentially exposed during November 20, 2021-March 18, 2022 who sought care within the military health system through February 24, 2023 was identified. Abstracted records were categorized as worsening preexisting or persistent new for conditions and symptoms. RESULTS: Of 653 medical charts reviewed, 357 (55%) had worsening preexisting or persistent new conditions or symptoms. Most-documented conditions included worsening preexisting migraine (8%; 50/653) and chronic pain (4%; 26/653), and persistent new migraine (2%; 14/653) and adjustment disorder (2%; 13/653). Most-documented symptoms included worsening preexisting headache (8%; 49/653) and anxiety (6%; 42/653), and persistent new rash (7%; 46/653) and headache (5%; 34/653). CONCLUSIONS: Approximately half of the abstracted medical records demonstrated worsening preexisting or persistent new conditions or symptoms and might benefit from sustained access to physical, mental, and specialized health care support systems. Continued monitoring for long-term health outcomes is recommended.