FAQ
Updated on 10/08/2025
WHY AM I RECEIVING A “DO NOT DRINK WITHOUT TREATMENT ADVISORY?”
The Guam Environmental Protection Agency (GEPA) established an Interim Action Level (IAL) for dieldrin effective August 1, 2025. Customers served by well Y-15 received an advisory via mail because water distributed to the Santa Rosa area is from a specific groundwater source that has a running annual average of either 0.2 micrograms per liter (μg/L or parts per billion – ppb) or 0.5ppb. These levels represent GEPA’s IAL for short- and long-term exposure. GWA must issue advisories based on GEPA’s IAL compliance requirements.
WHO IS AFFECTED BY GEPA’S IAL?
GWA supplies water to approximately 43,780 accounts. 1,112 rate payers received an advisory that water supplied to their location has dieldrin concentrations levels that are at, or exceed GEPA’s IAL.
WHAT IS DIELDRIN?
Dieldrin is a federally unregulated, manmade chemical used as an insecticide and termiticide from the 1950s until 1987. Dieldrin production ceased in 1987.
WHY IS DIELDRIN A CONCERN IF IT IS NO LONGER PRODUCED?
Dieldrin is considered a persistent organic pollutant because it does not easily break down and can remain in the environment for long periods of time – especially in soil and water. Dieldrin has also been identified as a probable carcinogen by the US EPA and exposure in trace amounts over an extended period of time may increase the likelihood of developing cancer.
HOW DOES DIELDRIN MAKE ITS WAY INTO DRINKING WATER?
The source of dieldrin contamination in Guam is unknown. We speculate that areas in Guam where dieldrin may have been applied as a termiticide have been disturbed as a result of construction and development. This disruption subsequently exposes potentially contaminated soil to rainfall – causing dieldrin to percolate into our groundwater sources.
We also speculate that excavated material or construction and demolition debris transported and disposed at hardfill sites have the potential to leach into groundwater sources since hardfills in Guam are not lined.
DO ALL OF GUAM’S WATER SOURCES HAVE HIGH LEVELS OF DIELDRIN?
No. Dieldrin has not been detected at levels at or above GEPA’s IAL in 97 of 99 GWA wells. GWA samples water at entry points in our distribution system on a quarterly basis. GWA tests for multiple bacterial, chemical and radiological contaminants in accordance with the Safe Drinking Water Act and the National Primary and Secondary Drinking Water Regulations.
Every July, GWA produces and distributes a drinking water quality report known as the Consumer Confidence Report (CCR). Dieldrin and other contaminants are reported in the CCR.
For more information on water quality, visit guamwaterworks.org/compliance-and-safety to access reports as far back as 2007.
IF MY WATER HAS DIELDRIN, WHY AM I STILL RECEIVING WATER?
At this time, GWA has not received compliance orders from either GEPA or US EPA to shut off water services to areas in Guam receiving water at or above GEPA’s IAL for dieldrin. GEPA has not issued any advisories against using your water for showering, washing dishes, laundry, irrigation or water activities. Based on GEPA’s compliance requirements, water exceeding their IAL for dieldrin must not be consumed without treatment. Shutting off water may cause more severe and immediate public health risks by diminishing hygiene and sanitation.
CAN GWA TEST MY WATER FOR DIELDRIN?
No. At this time, Guam does not have the local laboratory capacity to test for dieldrin. Samples are shipped to a US EPA certified water quality laboratory off island for analysis.
HOW CAN I REDUCE MY RISK OF EXPOSURE TO DIELDRIN IN MY WATER?
Most chemical contaminants can be removed or reduced through reverse osmosis (RO) treatment or granular activated carbon (GAC) filtration treatment. Even water with concentrations of unregulated contaminants like dieldrin can be treated through these systems.
If this is not an option for you, then consider using filtered or bottled water from a drinking water vending source that is both approved by the Department of Public Health and Social Services that employs both granular activated carbon and reverse osmosis processes.
You can also use a Point of Use (POU) device treatment device installed at a single faucet or spigot. Ensure that POU devices, RO and GAC filtration systems are NSF-53 or 401 certified.
Unfortunately, boiling your water will not get rid of dieldrin in the water.
WHAT IS GWA DOING TO ADDRESS DIELDRIN?
Source water treatment systems are under construction. Since late 2023, GWA has been working diligently to install the approved treatment system at affected well sites.
Funding for the $6.4M system improvement was obtained and design work has been completed. A construction contractor has been selected for the work and completion is slated for summer 2026.