This report about the quality of the City of Rockville’s drinking water is required by the United States Environmental Protection Agency and the Maryland Department of the Environment. Paper copies are available in City of Rockville facilities, including Rockville City Hall and recreation centers. If you would prefer a paper copy of the Drinking Water Quality Report mailed to your home, please call 240-314-8500. For more information, please contact James Boone, water treatment plant superintendent, at 240-314-8556 or jboone@rockvillemd.gov.
Annual Drinking Water Quality Reports
Frequently Asked Questions
The City of Rockville’s drinking water is safe, as set forth in the Environmental Protection Agency (EPA) regulations and adopted and enforced by the Maryland Department of the Environment (MDE). For the 2025 calendar year, the city’s water met or exceeded all water quality requirements.
The Water Quality Data Table below lists all the drinking water contaminants that were detected. None of these contaminants exceeded the drinking water standards. This report will help to inform you about the quality of your water and includes details about where your water comes from, what it contains and how it compares to standards set by state and federal regulatory agencies.
Drinking water, including bottled water, may reasonably be expected to contain small amounts of some contaminants. The presence of contaminants do not necessarily indicate that water poses a health risk. More information about contaminants and potential health effects is available by calling the EPA Safe Drinking Water hotline at 1-800-426-4791.
The sources of drinking water (both tap water and bottled water) include rivers, lakes, streams, ponds, reservoirs, springs and wells. As water travels over the surface of the land or through the ground, it dissolves naturally occurring minerals and can pick up substances resulting from the presence of animals or human activity, including:
- Inorganic contaminants, such as salts and metals, which can occur naturally or result from urban stormwater runoff, industrial or domestic wastewater discharges, oil and gas production, mining or farming.
- Radioactive contaminants, which can occur naturally or result from oil and gas production and mining activities.
- Microbial contaminants, such as viruses and bacteria that may come from wastewater treatment plants, septic systems, agricultural livestock operations and wildlife.
- Pesticides and herbicides, which may come from a variety of sources such as agriculture, urban stormwater runoff and residential uses.
- Organic chemical contaminants, including synthetic and volatile organic chemicals, which are byproducts of industrial processes and petroleum production, and can also come from gas stations, urban stormwater runoff and septic systems.
In order to ensure that tap water is safe to drink, the EPA prescribes regulations that limit the amount of certain contaminants in water provided by public water systems. Food and Drug Administration regulations establish limits for contaminants in bottled water, which must provide the same protection for public health.
Some people may be more vulnerable than the general population to contaminants in drinking water. Immunocompromised individuals, such as those with cancer undergoing chemotherapy, people who have undergone organ transplants, people with HIV/AIDS or other immune system disorders, and some elderly and infants can be at risk from infections. These people should seek advice from their healthcare providers about drinking water. EPA and the Centers for Disease Control issue guidelines on appropriate measures to reduce the risk of infection by cryptosporidium and other microbial contaminants. Call the EPA Safe Drinking Water hotline at 1-800-426-4791 for more information.
Lead can cause serious health problems, especially for pregnant women and young children. Lead in drinking water is primarily from materials and components associated with service lines and home plumbing. The City of Rockville is responsible for providing high-quality drinking water and removing lead pipes, but cannot control the variety of materials used in plumbing components in your home. You share the responsibility for protecting yourself and your family from the lead in your home plumbing. You can take responsibility by identifying and removing lead materials within your home plumbing and taking steps to reduce your family’s risk. Before drinking tap water, flush your pipes for several minutes by running your tap, taking a shower, doing laundry or a load of dishes. You can also use a filter certified by an American National Standards Institute-accredited certifier to reduce lead in drinking water. If you are concerned about lead in your water and wish to have your water tested, contact James Boone, water treatment plant superintendent, at 240-314-8556 or jboone@rockvillemd.gov. Information on lead in drinking water, testing methods and steps you can take to minimize exposure is available at epa.gov/safewater/lead.
The city’s primary source of water is the Potomac River. When Rockville’s water plant is not operating because of necessary improvements or maintenance activities, or in cases of regional drought, Rockville purchases water from the Washington Suburban Sanitary Commission (WSSC). In 2025, Rockville purchased about 1.8 million gallons of water (approximately 0.12% of its annual production) from WSSC, which also receives its water from the Potomac River. Find its water quality report at wsscwater.com/waterquality.
The City of Rockville’s water treatment plant was put into service in 1958 and, at that time, was capable of producing 4 million gallons per day (MGD) of treated water. The plant was upgraded in 1967 to increase production to 8 million gallons per day. In the mid-1990s, and in 2017, additional upgrades to the plant were made to meet EPA and MDE regulations. Since then, an average of 5 million gallons per day of raw (untreated) water is withdrawn from the Potomac River, treated at the plant and distributed to the city’s water customers. Once at the plant, the water is put through a six-step treatment process to ensure it meets Safe Drinking Water Act standards. Once treated, the water is sent through a series of underground water lines and water storage tanks and to your faucet.
The river water is treated to remove suspended sediments, algae, parasites, pathogens and other contaminants through the following processes:
Screen
Water from the Potomac River is pumped through a screen to remove large debris such as sticks, leaves and rocks. If algae blooms are present in the raw water withdrawn from the river, it is treated with potassium permanganate.
Coagulation
Water is treated with chemical compounds that make small suspended particles stick together and settle out of the water. This particle conglomerate is removed from the water prior to filtration.
Sedimentation
Water is passed through a settling basin or clarifier, allowing time for mud, sand, metals and other sediment to settle out.
Filtration
Water is passed through a dual media (sand and anthracite) filter, which removes many remaining contaminants.
Disinfection
Chlorine is added to the water to kill and/or inactivate any remaining pathogens. Fluoride is added to prevent tooth decay and a corrosion inhibitor is added to preserve the pipes that deliver the water to homes and businesses.
To Homes and Businesses
The treated water is stored in two storage tanks and is gravity-fed to houses and businesses when needed. The water is sampled at the plant, in the distribution system and at the tap in homes and businesses for lead, copper, other potentially harmful contaminants, bacteria and residual chlorine.
MDE performed a source water assessment of the Potomac River as it applies to the Rockville water plant. The 2002 report may be obtained online or by contacting the Water Supply Program at MDE, 1800 Washington Blvd., Baltimore, MD 21230. You can also call 410-537-3589. For more information, visit the Maryland Source Water Protection Program.
The tables in this report contain many unfamiliar terms and abbreviations. To help you better understand these terms, we’ve provided the following definitions:
- Action Level (AL): The concentration of a contaminant that, if exceeded, triggers treatment or other requirements that a water system must follow.
- Action Level Goal (ALG): The level of a contaminant in drinking water below which there is no known or expected risk to health. ALGs allow for a margin of safety.
- Level 1 Assessment: A study of the water system to identify potential problems and determine, if possible, why total coliform bacteria have been found in the water system.
- Level 2 Assessment: A detailed study of the water system to identify potential problems and determine, if possible, why an E. coli MCL violation has occurred and/or why total coliform bacteria have been found in the water system on multiple occasions.
- Maximum Contaminant Level or MCL: The highest level of a contaminant allowed in drinking water. MCLs are set as close to the MCLGs as feasible, using the best available treatment technology.
- Maximum Contaminant Level Goal or MCLG: The level of a contaminant in drinking water below which there is no known or expected risk to health. MCLGs allow for a margin of safety.
- Maximum Residual Disinfectant Level Goal or MRDLG: The level of a drinking water disinfectant below which there is no known or expected risk to health. MRDLGs do not reflect the benefits of the use of disinfectants to control microbial contaminants.
- Maximum Residual Disinfectant Level or MRDL: The highest level of a disinfectant allowed in drinking water. There is convincing evidence that addition of a disinfectant is necessary for control of microbial contaminants.
- Treatment Technique or TT: A required process intended to reduce the level of a contaminant in drinking water.
- Variances and Exemptions: State or EPA permission not to meet an MCL or a treatment technique under certain conditions.
- Avg: Average. Regulatory compliance with some MCLs is based on a running annual average of monthly samples.
- ND: Non-Detect. Constituent was not present or was present at levels below the detection limit of the testing method.
- LRAA: Locational Running Annual Average.
- mrem: Millirems per year, a measure of radiation absorbed by the body.
- ppt: Parts per trillion or nanograms per liter (ng/L). One part per trillion is equivalent to a single drop of food coloring in 18 million gallons of water.
- ppb: Parts per billion or micrograms per liter (ug/L). Equivalent to one ounce in 7,350,000 gallons of water.
- ppm: Parts per million or milligrams per liter (mg/L). Equivalent to one ounce in 7,350 gallons of water.
- Picocuries per liter (pCi/L): A measure of the radioactivity in water.
- NA: Not applicable.
Water Quality Data
The tables below list all the drinking water contaminants that were detected during calendar year 2025. The presence of contaminants in the water does not necessarily indicate that the water poses a health risk. Unless otherwise noted, the data presented in this table is from testing done in calendar year 2025.
Contact
James Boone
Public Works Department
Water Treatment Plant
240-314-8556
jboone@rockvillemd.gov