Photo courtesy of the City of Post Falls. The tower is the subject of the Post Falls Rotary Club's Save the Water Tower restoration campaign.
July 30, 2026
What does it cost to permit an ADU in Post Falls? I asked the city.
This page is only useful if it's right. If you find a mistake, tell me and I'll fix it.
Post Falls publishes a fee schedule that says hooking up new water and sewer service costs about $13,000 before anyone digs a hole.
My ADU will owe none of it.
Here's the short answer for a Post Falls lot that already has a house on it: an ADU has to connect to the existing water and sewer service, so it owes no additional capitalization fee. What it owes instead is ordinary permit fees, which the city estimates at $1,000 to $2,000 total.
That's our old water tower up top. It served the city's water system for more than 70 years before it was retired, and the Post Falls Rotary Club is raising money to restore it now. This post is about water and sewer, so it seemed like the right picture. If you want to help, they're at savethewatertower.com.
Let me show you the number I started with.
The $13,000 I thought I was looking at
The city's fee schedule is a public PDF, revised 10-1-2025. Water and sewer inside city limits are city utilities, run by Utility Billing and Public Works, so this document is where the numbers live. For a typical residential service it lists:
- Water capitalization fee, ¾" to 1" service: $3,278
- Sewer capitalization fee, one service unit of 5,000 gallons: $7,621
- Typical dig-in fee to install a 1" service: $2,351.25
- Sewer connection fee: $5. Utility deposit: $60.
That totals about $13,315 for a new residential water and sewer service, at the smallest published line size, before any actual construction charge.
Here's the question: Does a second dwelling on a lot that already has service count as a new connection?
I couldn't find anything in the city's fee schedule to answer that. So I emailed and asked.
The answer, in one sentence
I sent the question on July 5 to the Utility Billing Supervisor. Tisha Gallop, a Permit Technician with the City of Post Falls, replied on July 7:
"An ADU will need to be connected to the main house utilities for water and sewer, therefore there will be no additional capitalization fees."
Not a discount. Not a waiver I had to apply for. The ADU isn't a new connection, so the new-connection fees never attach in the first place.
Then what do I actually pay?
I wrote back the same day and asked what else to expect. Her answer, on July 8: an ADU is permitted like a remodel on your house. Not a special ADU process with its own fee, just the usual permits on the same schedule.
- Building permit, including residential plan review, based on value per square foot
- Plumbing permit for the ADU structure, based on fixture count
- Plumbing permit for the outside underground water and sewer line, usually $51
- Electrical permit, based on the square footage of the ADU
- Mechanical permit, based on fixture count
Her total: "Total permit fees might be between $1,000 to $2,000 (on the high side)." Inspections are included in the permit price. The one thing that costs extra is a $100 reinspection fee, per incident, if you keep scheduling an inspection before the work is ready.
I'll keep you updated on the actual permit fees as they come in, but this range is helpful.
What projects does this apply to?
It applies to a lot inside Post Falls city limits that already has a primary residence connected to city water and sewer. Mine does. If you are on unincorporated Kootenai County land, the answer may be very different. Post Falls has a patchwork of holes of county property throughout.
Take a look at the city's own zoning map. Everything colored is zoned by Post Falls. The white pockets inside the city's boundary are county land, and there are a lot of them.
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City of Post Falls zoning map, revised July 2, 2026. Click it to enlarge, or download the full PDF to zoom in on your own street. The city publishes it on its geospatial hub at post-falls-geospatial-hub-postfalls.hub.arcgis.com/pages/planningland-use. The map carries its own disclaimer that it is for reference only, so confirm with Post Falls Planning before you count on it for a specific parcel.
Three things I still don't know, all of which could add cost:
- Whether the existing water line and meter can carry both units. The no-fee answer covers fees. It says nothing about whether the physical service is big enough for a house plus an ADU, or who pays if it isn't.
- Whether the ADU gets its own utility bill or everything runs through the main house's account.
- What Avista will charge for electric and gas. Avista is my electric and gas provider, and unlike city water and sewer it is an investor-owned utility, not a city department. It publishes no fee schedule for this at all, because the cost depends on what infrastructure is already at your address. I submitted their construction request form on July 5 and they acknowledged it on July 7. A rep called me on July 10 and we have been playing phone tag since. Last I heard, the person who can answer it is out of the office until August 3.
So the honest running total for my build, today: about $1,000 to $2,000 to the city, $0 in water and sewer connection fees, and a question mark on the power and gas. I'm tracking every number on this build as it comes in, if you want to see where it stands today.
The $13,315 was sitting in a public document the whole time. It just wasn't my number, and nothing published anywhere said so. Getting the real answer took two emails and three days. Now it's on the internet where the next person can find it.
I'll post Avista's number the day I get it.
Sources: City of Post Falls fee schedule (PDF), revised 10-1-2025, read 2026-07-04; Utility Billing Division and Public Works (postfalls.gov); the City of Post Falls zoning map, revised 7-2-2026, published on the city's geospatial hub and also hosted here so the version I'm pointing at stays available; Avista, my electric and natural gas provider, construction request submitted 2026-07-05 and acknowledged 2026-07-07, no cost answer yet; and the Post Falls Rotary Club's Save the Water Tower campaign. The two quotes are from emails Tisha Gallop, Permit Technician, City of Post Falls, sent me on 2026-07-07 and 2026-07-08, both quoted verbatim above. They are direct replies to questions I asked, so there is no public URL to link to.
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