Defense officials aren’t able to determine how many people at military installations are drinking contaminated water because they don’t have complete data, according to a new government report.

This also limits the Defense Department’s ability to analyze the nature and length of the contamination, and to know what’s being done to correct the problem, according to the report from Government Accountability Office auditors.

Military departments didn’t report all health-based water violations to DoD, as is required by DoD policy, the auditors found.

About 3 million people in the U.S. receive drinking water from DoD public water systems, which must comply with regulations from states and the Environmental Protection Agency. Some systems provide DoD-treated water, while others provide water treated by other agencies.

GAO auditors found about 89 percent of those receiving DoD-treated water got it from a system with no violations. For non-DoD-treated water, the figure sits at 99 percent.

DoD must analyze the discrepancy and take any actions needed to address the causes, auditors stated.

In their analysis of Defense Department data for fiscal years 2013 through 2015, GAO auditors found the DoD public water systems complied with EPA and state health-based drinking water regulations “at levels comparable with other systems in the United States.” GAO has previously reported that states have generally under-reported violations, so EPA’s data system may not contain all public water system violations.

DoD policy requires the services to report annually on their installations’ public water systems’ compliance with health-based regulations. Officials are supposed to report to the assistant secretary of defense for energy, installations and environment. In the analysis of data from those three years, GAO auditors found that 77 installations reported violations to DoD, and 16 additional installations reported violations to the EPA but not to DoD.

DoD will evaluate the compliance differences between the types of DoD drinking water systems, stated Lucian Niemeyer, assistant secretary of defense for energy, installations and environment, in the DoD response, which agreed with GAO recommendations. DoD and the services also will clarify reporting on these health-based violations, he stated.