This question comes up on every single ADU we draw. Somewhere between the first sketch and the permit submittal, the client asks: "Does the casita need its own meter?" The honest answer is that it depends on three things, in a specific order — your city, your utility, and what you plan to do with the unit. Get that order wrong and you'll either spend thousands you didn't need to, or design yourself into a corner you have to redraw out of. Here's how it actually works in Arizona.
The short answer
Arizona state law does not require a separate meter for an ADU. The statute that legalized casitas statewide — A.R.S. § 9-461.18, created by HB 2720 — says nothing at all about utility meters, connections, or hookups. It is silent on the subject.
That silence is the whole story. Because the state didn't decide, two other parties do: your city, through its ADU ordinance and its water and wastewater policies, and your utility — SRP, APS, Southwest Gas, and whoever provides your water and sewer. Those two parties don't always want the same thing, and neither one calls the other to compare notes. That's your job, and it needs to happen before the plans are drawn, not after.
The three setups, defined properly
People use these three terms loosely and then get surprised at the utility counter. They aren't variations on a theme — they're structurally different arrangements with different owners, different bills, and different legal footing.
1. Separate meter (separate service)
The ADU gets its own utility-owned meter, its own account number, and its own bill. The utility reads it, bills it, and can connect or disconnect it independently. The tenant can put the account in their own name. This is a real second service on the property.
2. Submeter
There is one utility meter for the whole property. Behind it, you install a private meter on the line feeding the ADU. The utility doesn't own it, doesn't read it, doesn't bill it, and won't fix it. You read it, you do the math, and you bill your tenant. It's a measuring device, not a utility account.
3. Shared service
One meter, one bill, no measurement of the ADU's share. The casita is fed from the main house's service through a subpanel. Whoever's name is on the account pays for everything and sorts it out privately — flat rent, a fixed utility add-on, or nothing at all.
What SRP and APS actually do
Here's the part most homeowners have backwards. Neither SRP nor APS requires a separate meter for a casita, and neither one refuses to set one. They are not the gatekeeper. If your city has permitted a second legal dwelling unit on the lot and you want a second service, both utilities will establish one — as long as the service and meter location is approved by them before any electrical work goes in the ground.
That last part is where projects get expensive. SRP's electric service specifications are explicit that customers wanting a new meter installation or relocation contact SRP for an approved service and meter location prior to proceeding with any electrical installation, and construction projects route through SRP's Project Plan Portal. APS handles new or upgraded facilities through its line extension process under Service Schedule 3, where you receive a sketch of the extension facilities and an itemized cost quote based on their schedule of charges. Both processes take time. Neither one is fast if you start it the week before you want power.
A second meter is a permanent monthly cost
The part nobody budgets for: a second service is a second account, and a second account carries its own fixed monthly charge forever — whether the casita is occupied or empty.
SRP's monthly service charge moved to a tiered structure starting with the November 2025 billing cycle: roughly $20 for an apartment, condo or townhome, $30 for an average single-family home, and $40 for a larger-than-average home with high usage. Solar customers sit higher. On the APS side, a residential customer on the Fixed Energy Charge Plan pays a daily service charge — about $0.458 per day, which works out to roughly $14 on a 31-day month.
Call it a few hundred dollars a year in fixed charges you didn't have before, on top of the install. For a casita your mother-in-law lives in, that's money burned. For a unit you'll rent for twenty years, it's noise. Which is exactly why the answer depends on what you're doing with the unit.
One regulatory note worth knowing: APS is a public service corporation regulated by the Arizona Corporation Commission, so its rates and service rules live in ACC-approved tariffs. SRP is a political subdivision of the state — its prices are set by its own publicly elected board, not the ACC. That's why the two utilities' rules and rate structures don't mirror each other, and why "my buddy in Gilbert did it this way" isn't a reliable guide if your buddy is on the other utility.
The rooftop solar trap
This is the single most expensive mistake we see on Arizona ADUs, and almost nobody catches it in time.
Solar credits stay on the meter the array is connected to. They don't roll across two meters on the same property. Arizona doesn't have residential meter aggregation.
So picture the common Valley scenario. You have panels on the main house, sized to your household's usage. You build a casita and give it its own meter. Now the ADU buys every single kilowatt-hour at full retail price, while your main house — which just lost the evening load that used to soak up its production — exports more surplus than before at an export rate well below retail. You've simultaneously created a new full-price load and devalued your own solar production. The panels are right there on the roof, thirty feet away, and legally they can't help.
If you have rooftop solar, or you're planning it, shared service is usually the better economics — the ADU's load sits behind the same meter and gets consumed by your own generation first.
There's a flip side, and it's worth saying plainly. If you're an SRP customer on a demand price plan, stacking the ADU's load behind your main meter also stacks its usage onto your on-peak demand. A casita running its own AC during the afternoon peak can push your demand charge up in a way that shows up every month. That's not a reason to avoid shared service — it's a reason to look at your price plan and your actual usage pattern before you commit, and possibly to change plans when the unit comes online.
Submetering in Arizona: what's legal
If you're renting the ADU and you want the tenant to pay for what they use without the cost of a second service, submetering is the middle path — and Arizona law is clear about what you can and can't do.
Under A.R.S. § 33-1314.01, a landlord who charges separately for a utility may recover the charges imposed on the landlord by the utility provider, plus an administrative fee for the landlord for actual administrative costs only. No markup. No margin. No "utility fee" that quietly exceeds the bill. The statute also lays out the paperwork:
- The rental agreement must contain a disclosure listing the utility services that are charged separately and specifying the amount of any administrative fee.
- For an existing tenancy, you must give at least 90 days' notice before you begin using a submetering system or allocating costs.
- The statute also permits ratio utility billing — allocating cost per tenant, proportionately by livable square footage, per type of unit, or per number of water fixtures — as an alternative to a physical submeter.
What submetering doesn't get you is a utility that backs you up. The device is yours. If the tenant disputes the reading, that's your conversation, not SRP's. If it drifts or fails, that's your repair. Plenty of landlords run submeters happily for years — just go in knowing you've bought a job along with the hardware.
Your city decides more than your utility does
Because the state statute is silent, the real rules live in city ordinances and utility service policies — and they genuinely differ across the Valley. Here's what the published policies say in the three jurisdictions we work in most.
What it costs
Real numbers vary more than any blog post can capture — distance to the transformer, panel capacity, trench length, whether your driveway has to be cut and repaved. But two published figures are worth having in your head.
Water tap and meter. Phoenix publishes a full water service fee — a water tap and meter installation from a main in the right-of-way or easement — of roughly $1,753 for a 5/8-inch meter without paving, or about $3,041 with the paving fee. A 3/4-inch meter runs slightly higher. That's before any applicable development fees. It's also a good illustration of why Phoenix's shared-connection policy saves you real money rather than costing you convenience.
Electric. There's no published flat rate, because there isn't one. A second service can mean a new lateral, a trench, a meter pedestal, possibly transformer work or a main panel upgrade on the existing house. APS will prepare a preliminary sketch and rough cost estimate at no charge if you ask for one. SRP's Construction Contact Center handles the same conversation at 602-236-0777. Ask early — the quote is free and it's the single biggest swing factor in this decision.
And don't forget the load calculation. Even on shared service, adding a full second dwelling — its own AC, water heater, range, dryer — frequently pushes an older 100A or 125A house past its capacity. A service upgrade on the main house can cost as much as the second meter would have. That calc belongs in the design phase, not the inspection phase.
How to actually decide
Strip away the noise and it's four questions.
Building it for family? Share the service.
Multigenerational casitas are the easiest call in the book. One bill, lowest install cost, no second monthly service charge, no submeter to read. If your city allows it, share — and revisit it later if the use changes.
Renting it long-term? Submeter, or go separate.
Tenants who don't pay for power don't think about power, and in a Phoenix July that's a number you'll feel. A submeter with a compliant lease disclosure gets you accountability at a fraction of the install cost. Go to a full separate meter when you want the tenant on their own account in their own name and out of your billing entirely — worth it on a unit you intend to rent for the long haul.
Have solar, or planning it? Share, almost always.
Re-read the solar section. This one overrides most of the other logic.
Thinking about selling, splitting, or condo-izing? Separate.
If there's any real chance the ADU ends up on its own parcel or sold independently, a separate service is far cheaper to install during construction than to retrofit later. Trenching an open lot is easy. Trenching a finished, landscaped backyard is not.
The one thing to do before you draw anything
Make two phone calls. Call your city's planning department and ask what their ADU ordinance says about utility metering. Call SRP or APS and ask for a preliminary service sketch and estimate. Both calls are free, both take about fifteen minutes, and together they eliminate the most common source of mid-project redesign we see on casita work.
Do them before the plans are drawn. Utility routing, panel location, trench paths and meter placement all have to appear on the site plan you submit — and an inaccurate site plan is the single most reliable way to collect a round of city comments and lose three weeks.
We handle this part for you.
At SOKO Designs we draw ADUs and casitas across the Phoenix metro every week, and the utility question is baked into how we start a project — not something we discover at plan review. We'll tell you what your city requires, what your utility will actually do, and which setup makes financial sense for how you're going to use the unit.
If you're weighing a casita and want to talk it through before you commit, call us at 480-660-3133 or start a project. Bring your address and your last power bill — that's usually enough for us to give you a straight answer on the same call.
Utility rules, city ordinances, rates and fees change. Verify current requirements directly with your municipality, with SRP (602-236-8888) or APS (602-371-7171), and with your water and sewer provider before making design decisions. This article is general information, not legal or engineering advice.
