POTOMAC, Md. - Electricity has been restored to WSSC Water's largest drinking-water treatment plant after a power failure disrupted production Tuesday morning, but the utility is continuing an essential-water-use request affecting all 1.9 million customers in Montgomery and Prince George's counties while crews bring the facility fully back online.
WSSC Water issued the systemwide request at 8:45 a.m. after losing power at the Potomac Water Filtration Plant on River Road in Montgomery County.
The Potomac facility normally supplies drinking water to approximately 75% of WSSC Water customers, making the disruption significant even though the utility's other major treatment facility remained operational.
By 12:30 p.m., WSSC said electrical power had been restored and crews had begun the process of restarting plant systems.
The conservation request nevertheless remained in effect Tuesday afternoon because restoring electricity does not immediately return a large water-treatment facility to normal production.
WSSC said the request will remain in place until the Potomac plant is operating at full production and storage and pressure throughout the distribution system have stabilized.
Water remains safe to drink
WSSC emphasized that the water currently being delivered to customers remains safe to drink.
There is no boil-water advisory in effect, and customers do not need to boil water before drinking, cooking or other essential uses.
The emergency request is focused on preserving the quantity of treated water available in the system rather than responding to a known contamination problem.
WSSC has warned that reducing demand is important to maintaining adequate system storage, sanitation needs and water availability for firefighting.
The utility has also said conservation can help prevent conditions that could ultimately require a boil-water advisory.
Customers are being asked to take shorter showers, turn faucets off promptly, avoid all outdoor water use and lawn irrigation, limit toilet flushing and postpone use of washing machines and dishwashers when possible.
All WSSC customers in both counties are covered by the request, not only households that normally receive water produced at the Potomac plant.
What happened to the plant's electrical supply
WSSC's afternoon update provided a more detailed explanation of the electrical circumstances surrounding the outage.
The Potomac Water Filtration Plant receives electricity through two separate power feeds and is capable of operating fully using either one, according to the utility.
One of those two feeds had been removed from service in mid-September for routine maintenance being performed by Pepco.
That left the plant relying on the second feed Tuesday morning.
WSSC said an issue occurred with that second electrical feed early Tuesday, disrupting water production at the plant.
After the second feed failed, Pepco restored power to the feed that had previously been offline for scheduled maintenance.
That restoration allowed WSSC crews to begin bringing plant systems back online.
WSSC and Pepco were still investigating the cause of the failure involving the second electrical feed Tuesday afternoon.
Pepco said it remained in close coordination with WSSC because of the critical role the facility serves in the region.
Neither WSSC nor Pepco had publicly announced a specific cause for the electrical failure as of Tuesday afternoon.
There is currently no public evidence establishing that the outage resulted from a cyberattack, sabotage or any other intentional act.
A major gap in available water production
The scale of the conservation request becomes clearer when the two WSSC treatment plants are compared with normal customer demand.
WSSC told 7News that the Potomac plant typically produces approximately 100 million to 120 million gallons of drinking water each day.
Average systemwide customer demand is approximately 170 million gallons per day.
The Patuxent Water Filtration Plant remained operational throughout Tuesday's incident, but WSSC said that facility cannot meet the entire system's demand by itself.
WSSC's published infrastructure data lists the Potomac plant's maximum treatment capacity at 280 million gallons per day and the Patuxent plant's maximum capacity at 110 million gallons per day.
Together, the two facilities have a theoretical maximum production capacity of approximately 390 million gallons per day.
Those maximum design capacities do not mean either facility continuously produces at those levels.
During normal operations, production is adjusted to match system demand, storage requirements and operational conditions.
The Potomac plant's importance is therefore not simply its maximum capacity but the large share of WSSC's normal daily supply that it produces.
Why WSSC is asking customers to conserve after power was restored
Large drinking-water plants contain numerous treatment, pumping, chemical-feed, control and electrical systems that must be safely restarted and coordinated before normal production can resume.
WSSC said Tuesday afternoon that bringing all Potomac plant systems back online would take time.
Meanwhile, customers continue drawing water from the distribution network.
That network includes treated-water storage and thousands of miles of water mains that depend on sufficient supply and pressure.
WSSC operates nearly 5,900 miles of water mains and serves approximately 475,000 customer accounts across a service area approaching 1,000 square miles.
The essential-use request is intended to slow depletion of available treated water while production recovers.
Maintaining adequate pressure is also a public-health and fire-safety concern.
WSSC specifically said the conservation request is intended to protect fire protection, preserve system storage and reduce the possibility that a boil-water advisory becomes necessary.
Electrical reliability at Potomac was already an infrastructure priority
A review of WSSC planning and procurement documents shows that electrical reliability at the Potomac Water Filtration Plant was already the subject of significant capital investment before Tuesday's outage.
At a January 2026 budget presentation, WSSC identified a Potomac Water Filtration Plant power outage among its capital priorities and listed $4.5 million in proactive investment for electrical upgrades.
Separate commission documents from January show WSSC seeking approval for a much larger $15.99 million construction contract for what it calls the Potomac Water Filtration Plant Headhouse Power Feed project.
That project involves replacing the plant's USS-1 electrical substation and installing new switches, transformers, switchgear, underground electrical infrastructure and control connections.
WSSC's contract documents said the improvements were intended to increase electrical redundancy, improve fault isolation and strengthen the reliability of power serving critical treatment operations.
The commission package described the existing USS-1 substation as having deteriorated to a point where it could no longer reliably support plant operations.
The contract contemplated a 1,825-day construction period, equivalent to approximately five years.
Contractor W.M. Schlosser Company lists the $15.99 million Potomac power-feed project among its current projects.
Those records provide important context about ongoing efforts to modernize electrical infrastructure at the facility.
However, WSSC and Pepco have not said Tuesday's failure involved USS-1 or any component being replaced through the headhouse power-feed project.
The existence of the modernization project therefore should not be interpreted as proof of the cause of Tuesday's outage.
The plant is critical regional infrastructure
The Potomac Water Filtration Plant is located at 12200 River Road and draws raw water from the Potomac River before treating it for distribution across Montgomery and Prince George's counties.
Its treatment processes depend on substantial electrical power for pumping, sedimentation, filtration, chemical treatment, communications, process controls and other essential systems.
WSSC is Maryland's largest water and wastewater utility and the eighth largest in the United States, according to the utility.
It serves approximately 1.9 million people and maintains more than 11,000 miles of drinking-water and sewer infrastructure.
The utility says it performs approximately 500,000 laboratory tests each year to monitor water quality.
Its two drinking-water treatment plants draw from separate major watersheds: the Potomac River and the Patuxent River system.
That arrangement provides substantial treatment capacity and redundancy, but Tuesday's incident demonstrates how heavily normal operations depend on the much larger Potomac facility.
Power-feed redundancy was intended to prevent a full production interruption
WSSC's statement that the Potomac plant can operate fully on either of its two electrical feeds is significant.
Under normal circumstances, failure of a single feed should not necessarily halt plant operations because the second feed can supply the facility.
Tuesday's situation occurred while one feed was already unavailable because of scheduled Pepco maintenance and the remaining feed then experienced a separate problem.
That sequence temporarily eliminated the electrical redundancy on which the plant normally relies.
Pepco restored the maintenance feed after the second feed failed, returning electricity to the facility.
The cause of the second-feed failure remains one of the central unanswered questions in the incident.
It is also not yet clear when the feed that had been undergoing scheduled maintenance was originally expected to return to normal service.
No boil-water advisory as of Tuesday afternoon
Customers should distinguish WSSC's essential-water-use request from a boil-water advisory.
The utility has not told customers that the water is unsafe.
Instead, WSSC is asking customers to reduce demand while treatment production and the distribution system recover.
A boil-water advisory would be a separate public-health action and would include specific instructions from WSSC if conditions changed.
As of the latest Tuesday afternoon updates, no such advisory had been issued.
Customers should therefore continue following the essential-use restrictions without assuming the water currently at their taps is contaminated.
What customers should do now
WSSC is asking customers in both Montgomery and Prince George's counties to use water only when necessary until the utility formally lifts the request.
That means avoiding lawn irrigation and other outdoor use, reducing shower times, limiting unnecessary toilet flushing and delaying laundry and dishwasher loads when possible.
Residents should continue using water for drinking, cooking, hygiene, medical needs and other essential purposes.
Businesses and institutions served by WSSC are also covered by the systemwide conservation request.
Customers should watch for official WSSC updates before returning to normal water use.
What remains unknown
The most important unresolved issue is what caused the second power feed to fail while the other feed was undergoing maintenance.
WSSC and Pepco said Tuesday that they were jointly investigating that question.
Officials have not publicly provided an estimated time for full plant production to resume.
They also have not announced how much treated-water storage was available when the outage occurred or how close the system came to conditions that could have triggered a boil-water advisory.
The American Desk found no public statement connecting Tuesday's incident to the plant's ongoing $15.99 million electrical modernization project.
As of the latest update reviewed Tuesday afternoon, electricity had been restored, water remained safe to drink and the essential-water-use request remained in effect for all 1.9 million WSSC Water customers.