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Water Quality FAQs

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Yes. We perform 500,000 laboratory tests on our water every year, on samples from both of our water filtration plants and from 90 different locations throughout our distribution system. If there were a reason to believe the safety of our water was compromised, we would immediately issue a public notification via the news media, our own social media, and this website.

  • We add chlorine to the water to protect against microbial contamination as it travels from the filtration plant to your home or business. Average annual chlorine concentration in the distribution system can be found on our annual report.
  • We adjust chlorine seasonally and to respond to river conditions, so customers might on occasion notice the odor changes. For example, an increase from 1.0 mg/L to 1.5 mg/L might be noticeable to some customers, but is still within the normal range.

Chlorine Disinfects Drinking Water

Seasonal changes to the river can include algae that produce taste- and odor- causing compounds. We monitor levels carefully for geosmin and Methyl-isoborneol, which are common in our Patuxent reservoir and not harmful at the levels we detect.

  • Cross-contamination with the sewer system is extremely unlikely because drinking water is highly pressurized to prevent infiltration.
  • If you notice a sewer or sulfur smell in the cold water from all faucets in your home, please call 301-206-4002. A useful way to check is to take a clean glass and fill it with cold water from the tap, then walk into another room and check the odor again.
  • If you notice the odor only in the hot water, check your water heater for maintenance instructions. Water heaters need to be drained periodically, even when new. Instructions may vary, so please check the manufacturer and model specifications.
  • If you notice the odor only in specific sinks, check the p-trap under the sink

Customers often can interpret typical minor changes in chlorine in a variety of ways – for example, as metallic, acidic, or medicinal – but if you are concerned that the taste or odor has changed significantly, please call 301-206-4002.

Yes, discolored water is safe to drink, but we apologize for the occurrence and ask that you call 301-206-4002 to report it. We'll send a technician to flush the nearest fire hydrant to clear out the discoloration.

Our distribution system is largely made up of iron pipes, so disturbances to the system (such as construction, water main breaks, or water re-routing) can cause rusty-colored water. Note that it takes very little iron (0.2 mg/L) to discolor water and there are no adverse health effects associated with iron in drinking water. See our discolored water and flushing guidance pages for more information.

Washing machines are damp environments that can attract airborne bacteria or mold. We recommend leaving your washer open when it’s not in use. You might also periodically run a wash cycle with vinegar, rather than detergent, to disinfect the washer. But first check the manufacturer’s instructions.

Water heaters can attract sulfur-reducing bacteria, which cause a foul odor. We recommend fully draining your water heater annually, even if it is relatively new. Check the manufacturer’s instructions for maintenance.

Absolutely. We'll send bottles and instructions to your home and have you collect samples in order to capture the "worst-case scenario" of stagnant water. You'll fill two bottles with kitchen tap water and return them to us with the requested paperwork via FedEx. We’ll mail the test results to you in about three weeks. There is a $29.48 charge to cover the cost of the shipment.

Dissolved air in water can cause cloudiness, especially in the winter. Cold water can hold a lot of dissolved oxygen, and when the water leaves your faucet at room temperature, the oxygen forms tiny bubbles that make the water appear cloudy.

  • Fill a clear glass with COLD water and wait a minute for the glass to clear. If the cloudiness clears from bottom to top, the cause is air.
  • If the water does not clear after a few minutes, or clears from top to bottom, or if you see particles collecting at the bottom of the glass, please call 301-206-4002.

Lighting and background color can significantly affect the way customers perceive the color of their drinking water. Bathrooms often have bright lighting and with different bathtub colors and shades, it can appear that a tub full of water is bluish or greenish. If you’re concerned about the color of the water itself, fill a clear glass with water and hold it against a sheet of white paper in natural (outdoor) light.

Airborne and environmental molds and bacteria like to grow on damp surfaces, so it's common to see this type of buildup in bathrooms and around kitchen sinks. We recommend using bleach-based products for cleaning.

Yes, we test for harmful algae (also known as cyanobacteria) at both water plants. We test raw and treated water from summer into the fall.

Yes, we routinely test the water at our filtration plants for a range of synthetic organic compounds, including numerous pesticides. The results of those tests are available in our tap water analysis report.

We participate in a program called the Unregulated Contaminated Monitoring Rule, which targets specific contaminants under evaluation as emerging threats. Additionally, our scientists and engineers keep an eye on relevant research and available monitoring techniques to determine if and what we should consider for additional testing.

We treat our water to meet Environmental Protection Agency specifications for human consumption; pets, particularly fish, may be different. Please contact your vet if you are concerned about your pet’s health.

Last Modified: March 29, 2021, 1:12 pm EDT