How Much Does It Cost to Connect an ADU to Town Sewer?

By Buz Artiano, BuildX | April 2026

Watch: Bill Sims: What Builders Get Wrong About Real Estate Law | BuildX Podcast #24

You've already decided to build an ADU, and maybe you've started looking at floor plans, talked to a few builders, and now you've got a budget together. But when you hear someone talking about the sewer connection fee, you try to ask questions about it, but nobody can tell you what it actually costs, not even a ballpark, just "it depends." Well, that's a problem, because connection fees are in addition to your construction cost, they're completely different depending on where you live, and they can add tens of thousands of dollars to your project.

Hi, my name is Buz Artiano, I'm the founder and CEO of BuildX. We've built dozens of ADUs all over Massachusetts, but most of our projects are done in or around South Shore and Plymouth County. We do everything from design and permitting to dealing with local water departments, sewer commissions, and Board of Health offices on every project. We know what the fees are like because we pay them as part of our construction process. We do the same thing with properties that are on septic, we deal with the solution and permitting for those as well.

For some reason people don't really talk about sewer and water connection fees when it comes to building an ADU, but they should because those things are two of the biggest potential costs for the whole project. We've seen fees from $7,000 to $26,000 depending on where you live, what kind of connection you need, and how the town's pricing works. In this article we'll tell you what we know and what we've seen about connection fees, so you have the information you need to create a budget before you move forward.

How Much Do Sewer Connection Fees Actually Cost for an ADU?

The short answer is that sewer connection fees for a Massachusetts ADU can be anywhere from $7,000 to $26,000, it changes dramatically depending on where you live. The state itself hasn't set any standards or pricing. Every town gets to set its own rates, its own pricing structures, and its own rules about when and how you pay.

In Kingston, for example, the sewer connection fee is $26,000 and they do it as a package. They don't sell you the sewer connection based on how many bedrooms you are adding, they just have a fixed-rate package that covers up to three bedrooms. Whether your ADU has one bedroom or three, you pay the same amount.

In Norwell, the water connection fee by itself is $7,000. That's just the connection fee itself, it doesn't include any of the actual work of running the line to your property, you deal with that separately. And you have to pay it and get the water service established before you can submit a building permit application. You can't start building, or really do anything until the water department signs off.

On another build we just did, the water connection fee was $15,000! Again, that doesn't include any of the work to actually install it. That's more than double what the same connection costs if you go down the road to the next town. This stuff catches people off guard, it needs to be discussed so there are no unpleasant surprises.

Why Do Connection Fees Vary So Much from Town to Town?

Every Massachusetts town has its own water and sewer department, and they all set their own fees. There's no regulation by the state that says how much a town can charge for sewer or water. Because of that, fees can be $10,000 different from another depending on where you live.

Some towns charge a flat fee connection and it doesn't matter how many bedrooms you have. Some other places charge per bedroom or per gallon of estimated daily flow. Some towns bundle sewer and water into one fee, but others don't, which means you could be paying two separate connection fees, one for water, and one for sewer.

The pricing also depends on whether the town's system has available capacity. Towns that have older infrastructure or limited capacity will usually charge higher connection fees to help pay for much needed upgrades. Places that have recently expanded or upgraded their systems might not charge as much. The problem is that none of this information is out there and easy to find, which is why so many people don't know about them until partway through their project.

Are Sewer Connection Fees the Same as Water Connection Fees?

No. Sewer and water are usually separate departments in the same town, and they charge separate fees. The sewer connection fee lets you tie into the town's sewer main. The water connection fee is for access to the town's water supply. You'll have to pay both if your property is on town utilities.

If you're on town sewer, you might think you can just tie the ADU into the existing line. That's technically possible on some properties, but the town still charges a connection fee for the ADU. We warn people that being on city sewer doesn't mean the connection is free. Adding an ADU is the same as adding a second home, and the town treats that as a new connection.

If your property has town water but relies on a private septic system, you still have to pay the water connection fee. And you'll have to do a careful evaluation of your septic to see if it can handle the additional bedrooms. The water and sewer questions are related but they are two separate issues, and neither are free.

What If My Property Is Not on Town Sewer?

If your property is on septic rather than town sewer, it changes everything. You won't have to pay the town to connect the sewer line, but unfortunately the solution for a septic system can be even more expensive depending on if your current system can handle any additional flow.

Septic is the single biggest unknown cost when you're building an ADU on the South Shore. In most of the places that we work, the properties are on septic. That means most of our projects require a full septic evaluation as the very first step in our process, before we even talk about design. A failed perc test or a system that's too small can add $40,000 to $60,000 to the project. That's a huge number that has to be figured in from the beginning to make sure the project is even still viable.

We evaluate septic before we quote, because, like we've said, that one thing can up the entire project budget by a huge amount. Most builders don't include septic in their estimates. We do, because we hate seeing families commit to a project and then get an ugly surprise when they're told how much the septic solution will be. Sometimes they've already signed a contract and paid a deposit. You need to find out the condition and capacity of your septic before the first design meeting, it's the only way to figure out an accurate budget. If the septic work is just too expensive to make the project worth it, we'll tell you that upfront. It's not the most fun conversation to have, but it's the right one.

If you're trying to figure out if your property can support an ADU, it depends on two things. Whether you're on town sewer or septic, and if you're on septic, when was the system last inspected? That will tell you enough to estimate the largest single cost variable in your project.

Should My Builder Include Connection Fees in the Construction Quote?

Yes. A complete project quote should have everything that you'll pay listed right there on the paperwork. It should include everything you need to have a finished, permitted, move-in-ready ADU that is connected to all utilities. That includes sewer or water connection fees on top of the labor and materials to install them. If your builder's quote doesn't include sewer and water connection fees, the price is incomplete.

This is one of the most common issues that throws off an ADU budget. A family gets a quote of $250,000 and assumes that's all they have to pay. Then they find out that the sewer fee is $26,000, the water fee is $7,000, and the building permit is another $3,000. Now the project is $36,000 over budget, and all that could have easily been cleared up and included in the price from the beginning.

At BuildX, we check on any connection fees that might be applicable in your situation before we give you a quote. We call the water department, the sewer department, and the Board of Health in your town before we even try to tell you what the project might cost. When we quote a project, that's the number you will actually pay, not just the construction part of it. That's the difference between a quote and a budget.

How Do I Find Out What My Town Charges?

Call your town's water department and sewer department directly and ask them what the connection fees are for a new ADU. Some of them have published their fees on their websites, but a lot of them haven't, and the ones that do might not be updated for ADUs yet.

When we start a project in a town where BuildX has never built before, the first calls are to the building commissioner, the zoning office, and the utility departments. We need to find out what the town's specific requirements and fees are before we start working on design. In Norwell, for example, we learned that the water service has to be installed and paid for before we can submit a building permit application. Having to do things in that order is a requirement that affects the project timeline and cash flow, not just the cost.

If your builder hasn't made these calls, ask them to. If they can't tell you the sewer connection fee, the water connection fee, and the permit fee for where you live, your project budget isn't accurate.

Is Town Sewer Always Better Than Septic for an ADU?

Town sewer does make things simpler because there's no perc test, no septic design, no Board of Health approval for a new system, and no risk of a failed soil evaluation that can kill your project. If your property is on town sewer, the utility connections and installation are often much simpler and less expensive.

But "less expensive" doesn't mean cheap. A $26,000 sewer connection fee certainly isn't cheap. And if your property already has a septic system with extra capacity to add bedrooms, it can actually work out to be cheaper than connecting to town sewer, because you avoid the connection fee entirely and only pay for the labor to tie in the ADU to the existing system.

There's no answer that's right for every situation. It all depends on your property's existing infrastructure, your town's fees, and your project's total budget. We've built successful ADUs on town sewer, on upgraded septic systems, and on properties where the septic evaluation was the deciding factor in whether the project moved forward at all. Just make sure you know the number before you commit.

Know Your Connection Costs Before You Set Your Budget

Sewer and water connection fees are real costs that belong in your project budget from day one. They range from $7,000 to $26,000 or more depending on your Massachusetts town, and they are entirely separate from construction. If you want your project to be successful, know these numbers before you sign anything.