Montgomery County never opened its 2026 wet season for soil testing. The Department of Permitting Services soils testing page says it is no longer accepting applications for this year's wet season, "due to insufficient water table levels." On a Potomac property that cannot connect to public sewer, the County treats a lot as buildable only after satisfactory water table tests and percolation or sand mound testing establish a sewage disposal area. In practice, a buyer who goes under contract on a lot or teardown this fall and needs new soil testing has no test date in 2026.
That calendar problem sits on top of a broader point about well-and-septic Potomac. On these properties, the septic approval and reserve area set the limits on how large a house can be, how many rooms it can have and whether an addition gets approved. Zoning comes second.
A Calendar That Runs February to April
DPS says water table tests can only be conducted in a declared wet season, "typically February 1st thru April 15th," and only in years preceded by normal precipitation. Percolation and sand mound tests can happen any time of year once enough water table testing is complete. If the proposed tests sit in restrictive soil types, they also have to wait for the wet season. DPS may extend a season past April 15 if a sustained period of high water table levels develops, and it says it will announce any opening by email and on its website.
Measured from today, that puts the next typical window at February 2027, and only if the winter is wet enough. For a new site, the County's sequence runs in this order:
- DPS reviews the test layout before any testing begins.
- Water table testing takes place during a declared wet season.
- Percolation or sand mound testing follows, and DPS notes that "multiple visits may be required to obtain a sufficient number of satisfactory tests."
- A septic permit application goes in. DPS says complete, eligible applications are generally issued within two weeks.
Most of the time goes into the weather-dependent testing steps before the permit. Each soil visit also carries its own County fee. Montgomery County's FY 2027 well and septic fee schedule, effective July 1, 2026 through June 30, 2027, lists these:
| DPS service | FY 2027 County fee |
|---|---|
| Conventional percolation test | $970.11 per lot, per visit |
| Water table check | $547.24 per visit |
| Individual sewage disposal permit | $1,492.47 |
Because the fees are charged per visit, the totals grow with each test that has to be repeated. They also cover only the County's charges. Design, excavation and installation are billed separately by contractors.
How Much Ground a Septic System Needs
The testing matters because of how much land a septic system takes up. The Department of Environmental Protection says a new building lot normally needs an initial drainfield plus room for up to three reserve drainfields. The County estimates at least 10,000 square feet for a typical single-family home's initial and reserve areas combined. Septic systems and wells must also be at least 100 feet apart, and further setbacks apply to other site features.
All of that has to fit on the lot before the footprint of the house, the pool or a covered terrace is placed. DPS's building permit requirements for well-and-septic properties carry the same logic down to decks. Uncovered decks must stay 5 feet from septic components and reserve areas. Covered or enclosed decks need 15 feet from septic tanks and 20 feet from absorption areas. All decks must keep 10 feet from an existing or approved future well site.
The well has its own sign-off. DPS usually does not require testing before it issues a permit to drill, but it does require a flow test after drilling and before a building permit. The state minimum is 1 gallon per minute. A new or replacement well that supplies drinking water also needs Certificate of Potability sampling before the home's use-and-occupancy permit.
The Same Limit Applies to Renovations
Buyers who plan to keep the existing house and add to it face the same limit. The County's building permit submittal requirements for well-and-septic properties divide additions that add habitable space into three cases:
- A septic permit and an approved reserve area. The owner submits floor plans for the entire house so DPS can verify the system can handle the addition.
- A septic permit but no approved reserve area. The owner submits whole-house floor plans and a Habitable Space Worksheet.
- No approved septic permit or reserve area. The County says plainly that "an addition or alteration will not be approved."
The capacity check covers more than rooms labeled as bedrooms. It applies "when adding or redesigning rooms that could be used for sleeping purposes." So a lower-level guest suite, a home office with a closet or a finished attic can all come under review. Where a septic permit is required for the work, DPS says the septic work and its conditions must be finished before the building permit is approved.
For a buyer pricing a renovation into an offer, the important document is the property's septic permit and reserve-area record. The listing's bedroom count does not answer the question.
Whether Public Sewer Is an Option
The obvious alternative is to connect to public sewer, and that depends on the parcel's service category. Montgomery County gives every property separate water and sewer categories, and the two do not have to match. A home can have public water and an onsite septic plan. The County's category definitions break down this way:
| Sewer category | What it means |
|---|---|
| S-1 | Approved public service, generally existing or under construction |
| S-2 | Not used in the County |
| S-3 | Approved public service, generally requiring a new main extension |
| S-4 | Service planned in three to six years, generally requiring a capital project |
| S-5 | Service planned in years seven to ten, with private systems allowed in the meantime |
| S-6 | Public service not planned; development expected to use onsite systems |
Categories 1 and 3 work in both directions. These properties are eligible for public service, and the County generally requires public service for new development or for replacing an existing well or septic system. An interim onsite system has to connect within one year after public service becomes available. If a teardown switches to public water or sewer, every existing well and septic system must be properly abandoned before the County approves the permit.
Changing a category takes time. A category change request starts with an application to DEP. The case then goes either to an administrative track or to County Council review. DEP's typical hearing schedule is four to seven months for the administrative track and five to ten months for the Council track. Those timelines cover the hearing process only, not the construction of any main or the connection itself.
Potomac has its own limits on top of this. Under the 2002 Potomac Subregion Master Plan's peripheral policy, RE-1 and RE-2 properties at the edge of the sewer envelope are considered case by case. They qualify only if they abut or confront a property inside the envelope, and only if the extension follows existing rights-of-way without affecting streams, buffers or other sensitive areas. Piney Branch, Palatine, Greenbriar Preserve and the City of Rockville service area are excluded from that policy. The Glen Hills exclusion has been removed except for properties at the Piney Branch edge. Inside the Piney Branch restricted sewer area, service is limited to a list of exceptions, including documented septic failure. The exception for an abutting main allows a single hookup, which "cannot be used to support subdivision or resubdivision."
A Plan Update Timed to the End of This Council's Term
All of the above is in effect under the approved 2022 plan. A new version is moving through the Council now. On August 25, 2026, the County Executive sent the 2026 Executive Draft of the Water and Sewer Plan to the County Council. The County's schedule set the full Council resolution action for October 27. It also notes that this Council's authority over the Plan ends October 31, ahead of the November 3 election. The draft includes three provisions that matter for Potomac parcels:
- Abutting mains. As modified by the Maryland Department of the Environment, a new extension from an existing main is limited to avoiding an onsite environmental constraint. Additional connections are limited to qualifying failing systems or recorded lots that cannot use onsite systems. MDE rejected a provision that would have let an owner transfer a connection right from one qualifying property to another property under the same ownership.
- Palatine. A WSSC study found that a limited number of properties next to or facing Palatine's planned sewer envelope might connect to the low-pressure system, but only after the peripheral policy is revised. The draft also lists several individual category requests in the area as deferred.
- Pump-out rebate. A proposed fiscal year 2027 pilot would give owners a $100 rebate for pumping their septic tank at least once every five years. It replaces a mandatory pump-out approach the County says it is no longer pursuing.
Until the County posts the adopted text, these are draft provisions, and any of them could have changed in the final vote.
What Sellers Disclose, and What They Don't Have to Test
The seller's paperwork reflects the same split. Maryland's residential property disclosure form, revised August 3, 2026, asks whether the home has public water or a well and public sewer or septic. For septic, it asks the system type, whether it is known to work and the date it was last pumped. The form is based on the seller's actual knowledge, and the seller does not have to inspect the property to complete it. A seller may use the disclaimer instead, but known latent defects that pose a direct threat to health or safety must still be disclosed. Sales of unimproved property and sales where the buyer intends to demolish are exempt from the form. When a property-transfer septic inspection is done, MDE requires an appropriately licensed inspector and the State Standard Inspection Form. MDE does not say every sale must include one.
That leaves the scope of any inspection, and the time allowed for it, to the contract. For a teardown buyer, it also means the seller's form may not exist at all. The septic permit and reserve-area records are the more useful documents to request either way.
A Few Direct Questions
Is there an annual septic charge on the tax bill? Yes. Maryland's Bay Restoration Fund fee is $60 a year per septic user, and it is adjusted at settlement the same way property taxes are. The County's Department of Finance says owners with a septic system and no public water service are charged the fee on their property tax bill.
Will a replacement system need nitrogen-removal technology? Not automatically. Montgomery County has no state-designated Critical Areas. DPS may require best available technology case by case.
Where does a specific parcel's category come from? From the County's category map and DEP records for that address. A category describes one parcel, not the neighborhood around it.
This post is general information about public rules and is not legal, tax or financial advice. Please confirm the details of any specific property with the appropriate professional and with the County directly.
If you are weighing a Potomac teardown, an addition or a lot on well and septic, Lauren Pillsbury can help you collect the septic, reserve-area and category records before you set an offer price or contingency dates. Schedule a consultation to plan your timing around the County's 2027 soil-testing season.
