Potomac is home to the treatment plant that supplies most of Montgomery County's drinking water. The Potomac Water Filtration Plant sits near Swain's Lock, draws directly from the river, and can process up to 280 million gallons a day. Yet a meaningful share of the large wooded lots surrounding that plant, the ones along River Road, Falls Road, Persimmon Tree Road, and Seven Locks Road, never receive a drop of that water. Their homes run on private wells and septic systems, permanently, by county design.
That gap between what Potomac produces and what individual Potomac lots actually receive is the starting point for almost every closing delay I see in this neighborhood. The house shows well, the offer comes in strong, and then somewhere between contract and settlement, a question surfaces that has nothing to do with the kitchen or the roof: who inspected the septic, is that inspector still licensed under the new state rules, what does the HOA packet actually require, and is there a flood disclosure obligation for this particular lot. None of these are negotiation points. They're mechanical, and they run on their own clocks.
The county drew this line before your lot was ever surveyed
Montgomery County's Department of Environmental Protection assigns every property in the county a water category and a sewer category, numbered 1 through 6, as part of its Water and Sewer Plan. Categories 1 through 3 generally mean public service is available or already built out. Categories 4 and 5 mean public water or sewer is planned for the area but staged years or even a decade out, with WSSC declining to serve those properties until the capital project catches up. Category 6 is different in kind, not degree: development in a category 6 area is expected to rely on private, on-site systems permanently, with no plan for public service in the pipeline at all.
Most owners never look this up. There's no reason to, until a renovation triggers a permit review, or a sale puts a lender's underwriter in the loop asking whether the home is on public or private utilities. In Potomac, where estate-sized lots along the river corridor and out toward Darnestown were platted long before suburban water mains reached that far west, category 6 designations are common enough that they shape how a listing gets prepared, not just how it gets priced. A seller who assumes their neighborhood's affluence guarantees public water and sewer can be surprised to learn the county settled that question decades ago, on a map, independent of home value.
Maryland just changed who's allowed to sign off on your septic system
If your home sits on a well and septic system, the rules around who can inspect it changed this year. Legislation passed in the 2026 Maryland General Assembly session, tracked as SB165 and its House cross-file HB146, established licensing requirements for on-site wastewater property transfer inspectors under Title 9, Subtitle 11A of the Environment Article. Emergency regulations bridging the old system and the new one took effect December 31, 2025 and expired May 24, 2026, which means the licensing framework governing inspections today is the permanent one, not a temporary placeholder.
The practical effect for a seller is direct. According to the Maryland General Assembly, settlement on a contract cannot occur until both the seller and the buyer have received a report on the property transfer inspection. If you have a septic inspector you've used before, on a prior sale or a routine pump-out, confirm their current licensure before you schedule anything. An inspection performed by someone outside the new licensing structure isn't just a formality problem. It's a document your buyer's lender may refuse to accept at the settlement table, at the exact moment you have the least flexibility to fix it.
The same legislative package phases in a related requirement for landlords, who will need septic inspections and pump-outs completed by July 1, 2028, before new tenants occupy a property. That timeline matters less for a straightforward owner-occupied sale, but it's worth knowing if the Potomac property in question has ever been rented, since the compliance clock for that scenario is already running.
What your HOA is legally required to hand a buyer, and how long that takes
A meaningful share of Potomac's most recognizable communities, places like Avenel and River Falls, are built around private roads, shared entranceways, and HOA-maintained common areas rather than county-maintained streets. That arrangement is part of what gives these neighborhoods their consistency, but it also means the association, not the county, holds the paperwork a buyer's attorney will ask for.
The HOA resale disclosure package covers governing documents, current fees, pending assessments, financial statements, and meeting minutes. The association prepares the package. Once the buyer receives it, the review period can affect timing. If a private road resurfacing project or an entranceway renovation has been discussed at a board meeting but not yet billed, that's the kind of detail buried in those minutes.
Requesting the package the day you decide to list, rather than the day you go under contract, is the difference between the process running in parallel with your prep work and it running against your closing date.
Flood disclosures can vary from one Potomac property to another
Potomac's identity is tied to the river that runs along its southern edge, and flood-disclosure requirements can vary by property. Some areas of Cabin John, Glen Echo, and parts of Potomac closest to the water, including the river corridor near Persimmon Tree Road or MacArthur Boulevard, differ from a home a mile inland off Democracy Boulevard. Undisclosed water damage is consistently cited as one of the more common triggers for post-closing disputes in Maryland, precisely because it surfaces later, after a buyer has already moved in and experienced a wet season firsthand.
Why the tax proration matters more here than almost anywhere else in the county
Potomac's property assessments run well above the county average, with Potomac, Chevy Chase, and Glen Echo posting tax bills roughly 2.17 to 2.29 times the Montgomery County norm. That ratio isn't just a talking point about neighborhood value. It changes the stakes of a routine closing task: the property tax proration between seller and buyer. A small rounding error or a miscalculated effective date in the proration formula produces a modest dollar swing on an average-priced home. On a Potomac assessment running more than double the county average, the same percentage error is a materially larger number at the settlement table. It's worth confirming with your title company early how they intend to calculate the proration, rather than reviewing it for the first time on the settlement statement.
Before you list, walk through this
- Confirm your property's water and sewer service category through the county's mapping tool, particularly if your lot sits near a boundary between served and unserved areas.
- If you're on well and septic, schedule the transfer inspection early and confirm in writing that your inspector holds current licensure under the 2026 rules, since settlement can't proceed without the report.
- If you're in a private-road HOA community, request your resale package the day you decide to sell, not the day you accept an offer.
- If your lot touches the river corridor, confirm its flood zone designation before you sign the disclosure form.
- Ask your title company how they'll calculate your tax proration, given how much higher Potomac assessments run compared to the county average.
None of these five items will show up in a listing photo, and none of them will move your list price. What they will do is determine whether your contract closes on the date you signed up for, or thirty days later while someone tracks down a licensed inspector or a set of HOA meeting minutes.
A few questions worth settling before you list
Does every home in Potomac run on well and septic? No. Much of the neighborhood is served by WSSC public water and sewer. Whether a specific lot is on public service or private systems depends on the county's water and sewer category assignment for that parcel, not on the surrounding neighborhood's reputation.
Why request an HOA resale package early? Requesting it before you go under contract gives the association time to prepare it while you get ready to list.
Who is allowed to perform a septic transfer inspection now? As of the current licensing framework in effect in 2026, inspectors must be licensed under the state's on-site wastewater professional licensing structure. Settlement cannot occur until both the seller and buyer have received the inspection report.
If you're weighing when to list a Potomac property and want a clear read on which of these issues actually applies to your specific lot, Peter Maser can walk through your service category, your HOA's current packet timeline, and your disclosure obligations before you go to market. Request a Private Home Valuation and we'll start with the parts of your sale that have nothing to do with staging.
This article is general information, not legal, tax or financial advice. Consult a qualified professional about your situation.
