ADU Utility Connection Fees: Separate Meter or Shared Service?

An accessory dwelling unit that shares the main house’s water meter and sewer line usually owes little or nothing in connection fees. A separate meter is where the money is. In California, state law bars impact fees on an ADU with 750 square feet of interior livable space or less and treats most ADUs as no new residential use for water and sewer capacity charges (Gov. Code §66311.5, as renumbered by SB 543). Outside California the rules are local: Denver Water charges a detached ADU a flat $2,170 system development charge inside Denver from July 1, 2026, against $9,440 for a new house on a 6,000-square-foot lot (Denver Water 2026 SDCs), and Portland waives all of its system development charges for ADUs whose owners sign a 10-year no-short-term-rental covenant.

This article covers the ADU question only. For the fees themselves, see tap fee vs. impact fee and water meter installation cost.

Shared service or separate meter: what changes

Utilities measure new demand by the meter, so the meter decision drives the bill.

• Shared service, same meter. The ADU tees off the house’s water line after the meter and joins the house’s sewer lateral. No new tap or meter. Some utilities still charge a per-unit capacity fee; others charge nothing.
• Shared service, bigger meter. Extra fixtures can outgrow a 5/8- or 3/4-inch meter. Upsizing triggers the difference in capacity fees between the two sizes.
• Separate service. New tap, service line, meter and often sewer lateral, with the utility’s full installation charges and, outside California, usually a capacity fee. The payoff is separate billing.

Private runs add to every option. Our national estimates are $30 to $150 per foot for a water service line and $50 to $250 per foot for a sewer lateral, so 60 feet of both to a backyard unit comes to an estimated $4,800 to $24,000 (60 × $80 to 60 × $400). See water service line cost and sewer lateral cost.

California: what state law allows utilities to charge

California’s ADU fee rules were long found in Government Code §65852.2 and were later recodified as §66324 in a separate ADU chapter of the code. Senate Bill 543 (Chapter 520, Statutes of 2025), signed October 10, 2025, amended that section and renumbered it §66311.5, effective January 1, 2026 (SB 543 chaptered text). Its rules, as of September 2026:

1. Not a new residential use. A city, special district or water corporation may not count an ADU or junior ADU as new residential use when it calculates water and sewer connection fees or capacity charges, unless the unit is built together with a new single-family home.
2. No impact fees on small units. None on an ADU with 750 square feet of interior livable space or less, or a junior ADU of 500 square feet or less; SB 543 added both the “interior livable space” measure and the junior ADU threshold. Larger ADUs pay impact fees in proportion to the primary home’s square footage. The statute excludes connection fees and capacity charges from “impact fee”; the next two rules cover those.
3. Conversions: no separate connection. For an ADU or junior ADU inside the existing or proposed space of a house or existing accessory structure (up to 150 square feet of expansion for access), the utility may not require a new or separate connection or charge a related connection fee or capacity charge, unless the unit is built with a new house or the ADU is later conveyed separately.
4. Other ADUs: separate connection allowed, fee proportional. For any other ADU, such as a new detached unit, the utility may require a new or separate connection directly to the ADU. Any connection fee or capacity charge must be proportionate to the unit’s burden, measured by its square footage or its drainage fixture unit (DFU) count under the Uniform Plumbing Code, and may not exceed the reasonable cost of providing the service.

Example: a 900-square-foot ADU behind an 1,800-square-foot house can be charged impact fees at 900 ÷ 1,800 = 50% of the house rate. At 740 square feet, $0.

For scale, the City of Sacramento’s FY2026-27 single-family charges are a $10,513.13 water development fee for a 3/4-inch meter, a $2,670.74 or $5,936.84 sewer development fee depending on service area, and $4,507 plus $723 to install a 1-inch easement tap and meter (City of Sacramento Department of Utilities, effective July 1, 2026). A detached ADU’s capacity charge must be scaled to its own burden, so ask how the utility computes that share before choosing a separate meter. See also Sacramento tap fees.

Outside California: four real utility policies

ADU water and sewer rules at four utilities, as published September 2026. Amounts are one-time charges.

Denver: a flat ADU charge

Denver Water prices a new house by lot size: $3,380 plus $1.01 per square foot inside Denver from July 1, 2026, or $3,380 + (6,000 × $1.01) = $9,440 on a 6,000-square-foot lot. A detached ADU with its own sleeping, cooking and sanitation pays a flat $2,170 inside Denver and $3,030 outside (it was $2,055 and $2,870 from January 1 to June 30, 2026). A separate meter adds $265 for a 5/8-inch meter, $185 for the tap and $155 for inspection, or $605 before the plumber.

Denver sewer is billed by the city: $6,480 per unit ($410 city fee plus $6,070 Metro Water Recovery fee) for homes, duplexes and multi-unit buildings with individual water taps or a manifold (Denver DOTI 2026 sewer permit fees). The schedule does not say how an ADU is counted, so ask before you budget.

Portland: the SDC waiver, and what it does not cover

Portland City Code 17.14.070, last amended by Ordinance 192082 effective August 15, 2025, exempts ADUs from all system development charges, water and sewer included, if the permit intake date is August 1, 2018 or later and the owner records a covenant barring short-term rentals on the property for 10 years from final inspection (City Code 17.14.070; Portland ADU SDC waiver). A violation makes the SDCs due at 150% of current rates plus a $400 fee. ADUs are excluded from the city’s temporary SDC exemption for new housing permitted August 15, 2025 through September 30, 2028 (Portland housing SDC exemption).

The waiver does not cover construction: a new 1-inch Water Bureau service with meter is $8,464 without paving and $9,701 with it (FY2026-27). Without the waiver, add the $5,483 water SDC for a 5/8-inch meter and a sanitary SDC of 60% × $623 = $373.80 per drainage fixture unit (BES rates and charges); at an assumed 12 DFUs, 12 × $373.80 = $4,485.60.

Seattle: one service per parcel

Seattle Public Utilities generally allows one domestic water service per parcel, backyard cottages included, since the cottage is not on its own parcel. Owners can add a private submeter, which SPU does not install or read. The question is whether the shared meter must grow. The 2026 SDC, water plus wastewater, is $9,500 for a 3/4-inch meter and $16,150 for 1-inch, with credit for existing service (SPU SDC, effective Jan. 1, 2026). If the credit equals the 3/4-inch charge, the upsize costs $16,150 − $9,500 = $6,650, plus $4,975 to $6,350 if SPU must install a new 1-inch service (SPU Director’s Rule FIN-220.2, 2026). Confirm the credit with SPU.

Austin: service units make meter size the cost driver

Austin Water charges impact fees per service unit: a 5/8-inch meter is one unit, 3/4-inch 1.5 and 1-inch 2.5. Each unit costs $4,800 water plus $2,900 wastewater on lots platted since October 1, 2023, and $4,700 plus $2,500 on lots platted October 1, 2018 through September 30, 2023; older plats pay lower zone-based fees we have not tabulated. A separate 5/8-inch ADU meter on a 2020 plat would carry $4,700 + $2,500 = $7,200 before meter and tap charges. We found no published Austin Water rule specific to ADUs, so ask the Utility Permitting Office how an ADU on a shared meter, or an upsize, is charged.

How to decide

1. Ask the water utility in writing whether an ADU on the existing meter owes a capacity charge and whether the added fixtures force a larger meter.
2. Price the upsize against a new small meter. In Austin both come from the same service-unit schedule: half a unit more for 5/8 to 3/4 inch, one unit for a second 5/8-inch meter.
3. Count the trench. The shorter run, street to ADU or house to ADU, often decides it. Use the utility connection cost calculator.
4. Think about resale. In California, separate conveyance of the ADU lets the utility require a separate connection and charge for it.
5. Check sewer separately. Water and sewer are often billed by different agencies, as in Denver and Portland. A water waiver or flat fee says nothing about the sewer charge.

For how fees are paid and when, see new construction utility costs and who pays tap fees. City-by-city numbers are at tap fees by city. If the ADU comes with a teardown of the main house, see existing-service credits on a rebuild.

Frequently asked questions