In February 2024, a 54-inch sewer pipe running through the woods near the Potomac Heritage Trail in Great Falls started to fail. It was not a small pipe. The Potomac Interceptor carries about 60 million gallons of wastewater a day from Loudoun and Fairfax counties, Montgomery County, and Dulles Airport, all the way to the Blue Plains treatment plant in Washington, DC. When the ground around Manhole 31 gave way, DC Water brought in bypass pumps and Fairfax County brought in a hydrogeologist, and for a stretch of that spring, eighteen private wells near the break got tested for bacteria.

Four of them came back positive for coliform. One came back positive for E. coli. The homes on those wells were not connected to the failed sewer line. They never had been. That is the point worth sitting with if you are comparing a Great Falls property to one in McLean or Potomac: the absence of a public sewer connection does not mean the absence of public infrastructure risk. It just changes what that risk looks like, and when it shows up.

Why "no water bill" is the wrong way to read the ledger

A large share of homes in Great Falls run on private well and septic systems rather than the public water and sewer lines that serve most of McLean, Bethesda, and Potomac. Fairfax County has reported more than 15,000 households countywide relying on groundwater wells, and Great Falls carries a disproportionate share of that number given its lot sizes and its distance from the nearest sewer main.

The appeal is obvious on paper. No monthly water bill. No sewer service charge creeping up every fiscal year. Fairfax County's own FY2026 budget shows the average public sewer customer's bill rising from $762.76 to $807.60, a 5.9 percent increase, with the per-1,000-gallon rate moving from $8.81 to $9.33. A Great Falls homeowner on well and septic pays none of that.

What they pay instead is lumpier, and in this soil, larger than most buyers expect. Great Falls sits largely on dense, poorly draining Type IV clay. That single geological fact does most of the work in determining what a septic system actually costs here, more than square footage or bedroom count on their own.

A national buyer researching septic costs online will often find figures in the $5,000 to $8,000 range. In Great Falls and neighboring McLean, that number is frequently just the starting point for the permit, not the system. Virginia sizes systems by bedroom count rather than square footage: a three-bedroom home typically needs a 1,000-gallon tank, a four-bedroom home needs 1,200 to 1,250 gallons, and the real cost driver is the larger drain field a four-bedroom system requires, roughly 20 to 25 percent bigger than the three-bedroom version.

None of that shows up in a median sale price. It shows up when a buyer's inspection contingency turns up a failing drain field on a five-bedroom estate, and the repair estimate lands closer to a car payment than a plumbing bill.

The pipe that proved the point

Routine maintenance is the predictable half of the septic and well equation. Virginia law requires tanks to be pumped at least every five years, and most Northern Virginia households do it every three to five years at a cost of $350 to $650 per visit. That part is manageable and well understood by anyone who has owned one of these homes for a while.

The Manhole 31 failure showed the other half: the part that is not under the homeowner's control at all.

"I can say that there is no conclusive evidence that Manhole 31 sewage contaminated these wells."

That was Christopher Herrington, director of Fairfax County's Department of Public Works and Environmental Services, at the community meeting held after the pipe failed. His statement was carefully worded, and it needed to be. Four wells tested positive for coliform bacteria, one of them, well number 9, six separate times. One tested positive for E. coli. Fairfax County's Health Department advised the affected households to boil their water and disinfect their wells, and Supervisor Jimmy Bierman told the room plainly that he was "not very happy with DC Water right now for a number of reasons."

Whether the sewage from Manhole 31 caused the contamination or the timing was coincidental, the county never fully settled it in public. What is settled is this: a private well thirty feet from someone else's failed public pipe is not automatically insulated from that failure. Groundwater does not check property lines. DC Water's own project page now shows the Manhole 31 reconstruction entering its final phase, so the specific break that triggered this episode is close to resolved. The underlying fact that a Great Falls well can be affected by an incident it had no connection to, no vote on, and no ability to prevent, is not something that gets fixed by finishing one pipe.

What this means at the negotiating table

For a buyer comparing a Great Falls estate to a similarly priced home in McLean or Potomac with public utilities, the well and septic question deserves the same weight as square footage or lot size. A few things to build into that comparison directly:

• Ask for the drainfield plat from the seller, or have your agent request it from the county. Without it, no one can confirm what bedroom count the system was rated for or where the reserve drain field sits.
• Ask for pump and inspection records, not just a recent pump-out. A system pumped on schedule for fifteen years tells a very different story than one with a single receipt from last month.
• Get a well water test as part of your due diligence period, not as an afterthought. The Great Falls Citizens Association coordinates with Fairfax County's Cooperative Extension office on well testing clinics precisely because so many residents share this exposure and so few think about it until something goes wrong.
• Understand that an alternative system replacement, should one come up in negotiations, is a five-figure conversation in this soil, not a four-figure one.

None of this is a reason to avoid Great Falls. The privacy, the acreage, and the character that draw buyers here come directly from the same low-density development pattern that kept public sewer lines from ever reaching most of the neighborhood. A 2010 proposal to extend sewer lines into Great Falls carried a price tag north of $7.5 million and a three-year timeline, and it never moved forward. That is not a gap waiting to be closed. It is a structural feature of the place, as permanent as the lot sizes themselves.

Reading the tradeoff correctly

The honest comparison is not "public sewer costs money, private septic is free." It is two different cost structures with two different risk profiles. Public sewer in Fairfax County means a rising monthly bill, currently averaging just over $800 a year, in exchange for a system someone else maintains and monitors. Private well and septic in Great Falls means no monthly bill and full control, in exchange for lumpy five-figure maintenance events and an exposure to nearby infrastructure failures that a McLean homeowner on public water never has to think about.

Buyers who understand that distinction going in negotiate differently. They budget for it. They ask the right questions during inspection. And they are not surprised eighteen months into ownership when a system that seemed fine at closing needs a five-figure repair, or when a headline about a DC Water pipe two miles away turns out to matter more than they expected.

If you are weighing a Great Falls property against homes in McLean, Potomac, or Bethesda, the well and septic question is worth a real conversation before you write an offer, not after. Amy Embrey and the Embrey Properties team walk buyers through exactly this kind of due diligence on every Great Falls contract. Schedule a consultation to talk through what a specific property's systems mean for your budget and your timeline.