Does code require low-flow toilets and fixtures in Arizona?

Two layers of limits apply in Phoenix, and the city's layer is the stricter one.

The federal numbers come from the Department of Energy's rules at 10 CFR 430.32, which apply to fixtures manufactured after January 1, 1994. Phoenix's numbers come from its amendments to the 2024 International Residential Code (Table P2903.2) and the 2024 Uniform Plumbing Code, which the city adopted with the rest of its 2024 building code. The amendments carve out exceptions where long piping or at-risk occupants raise the risk of waterborne pathogens such as Legionella, including buildings taller than six stories, larger buildings with certain water systems, custodial care and surgical or treatment areas, and housing for people under 2 or over 65. Those exceptions keep the federal-level numbers. A plumber or the city's permit desk can tell you which set covers your building.

The phrase low-flow gets used loosely, but in code terms it just means a fixture that meets these caps. The old fixtures these rules replaced were a different animal, and that gap is where the water savings come from. The rule reaches you twice: once at the store, where high-flow fixtures are off the shelf, and again at inspection, where new work has to meet the code in force where you live.

This is the point that trips up most homeowners. The code numbers above are the least efficient fixture you are allowed to install. They are the legal minimum. The WaterSense label, run by the EPA, is a separate voluntary program. Under the federal rules it sits well below the code line, and in Phoenix the 2024 code has now caught up to it:

• WaterSense toilets: 1.28 gpf or less (versus the 1.6 gpf federal cap)
• WaterSense showerheads: 2.0 gpm or less (versus the 2.5 gpm federal cap)
• WaterSense bathroom faucets: 1.5 gpm or less (versus the 2.2 gpm federal cap)

In Phoenix the 2024 code amendments now sit at those same numbers, and the city's stated reason for the change is that it is consistent with current WaterSense standards. Elsewhere in the Valley, the federal numbers are still the ceiling unless a city's own amendments say otherwise. WaterSense as a label is not required by code, but because the program saves more water, it is what almost every utility rebate is built around. If a rebate asks for a WaterSense toilet, a plain 1.6 gpf model outside the Phoenix exceptions will not qualify. The EPA says a WaterSense toilet uses 1.28 gallons per flush or less, which is 20 percent less water than the current federal standard of 1.6 gallons per flush, while still providing equal or superior performance. For how rebates work locally, see our page on Phoenix water-conservation rebates.

So three different bars exist, and it helps to keep them straight. The federal minimum is 1.6 gpf, 2.2 gpm faucets and 2.5 gpm showerheads. Phoenix's 2024 code and the WaterSense label are stricter, at 1.28 gpf, 1.5 gpm and 2.0 gpm. The rebate generally tracks WaterSense, not the code minimum, so check its terms before you buy.

For whether going below the code limit makes sense in your shower, see are low-flow showerheads worth it. For how a WaterSense faucet performs day to day, see do low-flow faucets work well.

The code applies to new construction and to replacements, not just to ground-up building. When you swap out a toilet, faucet, or showerhead, the new fixture has to meet the current flow limits. You cannot put in a salvaged or vintage high-gallon toilet during a bathroom remodel, even in an older home, because the replacement is new work under the code.

That matters most in homes built before 1994, when the federal standard took full effect. A toilet from that era can use up to 6 gallons per flush, nearly four times the current cap. The moment you replace it, you drop to 1.6 gpf at most under federal rules, and to 1.28 gpf under Phoenix's 2024 code. The water savings from that single swap are large. The EPA estimates that replacing older, inefficient toilets with WaterSense models can save a typical home about 13,000 gallons of water per year.

A few practical notes for anyone planning a swap:

• You are not required to upgrade fixtures you keep. The code applies when you install something new, not to a working old toilet you leave in place.
• Once you replace, you meet current code. There is no grandfather exception that lets you put in a high-flow fixture during a remodel.
• Measure before you buy. Flush valves come in different sizes, and a fixture's rated flow is printed on the unit and the box, so you can confirm it meets the cap before installation.

For what a swap typically involves, see our page on the cost to replace a toilet.

Fixture flow limits are national, but they land harder in the desert. Phoenix draws most of its supply from the Salt, Verde, and Colorado Rivers, sources that are stressed by long-term drought across the Southwest. The city has run water-conservation programs for years, and efficient fixtures are one of the simplest tools it has, because the savings are built into the hardware and do not depend on anyone changing their habits.

Toilets are the biggest single target indoors. The EPA reports that toilets account for nearly 30 percent of an average home's indoor water use, more than any other fixture. Holding new toilets to 1.28 gpf under Phoenix's code, and steering rebates toward WaterSense models, chips away at the largest slice of indoor demand. Across a city the size of Phoenix, that adds up fast.

This is also why the WaterSense versus code distinction is worth understanding rather than ignoring. Code keeps the worst fixtures out. WaterSense and the rebates that follow it push the average lower than code alone would. In a place where the supply is genuinely tight, the voluntary tier is doing real work on top of the legal minimum.

The flow caps are national in origin, but the plumbing code is adopted locally. Arizona cities each adopt a model plumbing code, usually a recent edition of the Uniform Plumbing Code or the International Plumbing Code, sometimes with local amendments. Phoenix adopted both the 2024 UPC and the 2024 IPC. The fixture flow limits carry through that adopted code, and the city building department enforces them through permits and inspections on new work.

That local adoption is why the exact code edition can differ slightly from one Arizona city to the next, even though the federal ceilings of 1.6 gpf, 2.2 gpm for faucets and 2.5 gpm for showerheads apply everywhere in the country. A city's amendments can go lower, as Phoenix's did. The edition affects details like venting and trap rules more than it affects fixture flow rates, which are set by federal law and any local amendment. To see which edition applies in Phoenix, read our page on what plumbing code Phoenix uses.

Waterless urinals are a separate question under the same codes, covered in are waterless urinals allowed in Arizona businesses.

For a homeowner, the takeaway is simple. Check the flow rating on the box before you buy. A 1.6 gpf toilet is still sold in stores, and it does not meet Phoenix's 1.28 gpf cap, so an installer working under a Phoenix permit will not be able to pass it. In Phoenix, a WaterSense model is effectively the code minimum for toilets, faucets and showerheads. In cities still on the federal numbers, a WaterSense model is what to look for if you want a rebate. If you are remodeling or replacing an old high-gallon toilet, the upgrade is required by code anyway, and the water and bill savings come along with it. For a room-by-room view of where indoor water goes, see how to conserve water inside your home.