IRC P3009 Graywater Systems: Arizona's Type 1 Reuse Permit

Reusing household drain water to keep a desert yard alive is one of the smartest moves an Arizona home can make, and the code has a place for it. IRC Section P3009 covers graywater soil absorption systems, which take drain water from a few household fixtures and put it underground to water plants. What surprises most people is how short the section is, and why.

What counts as graywater

Graywater is the lightly used water your home makes from washing, not from toilets or the kitchen. The code defines it as the:

Waste discharged from lavatories, bathtubs, showers, clothes washers and laundry trays.

Water from toilets, kitchen sinks, and dishwashers is not graywater. It carries waste, grease, and food, which makes it blackwater, and it has to go to the sewer or septic system. The dividing line matters because graywater can be reused with light handling, while blackwater cannot. For a plain-language breakdown of the sources, see the graywater glossary entry.

What P3009 actually requires

Here is the part that trips people up. P3009 does not spell out tank sizes, soil tests, or trench depths. It is a short section that points graywater soil absorption systems to the rules of the state authority that regulates them. The model code sets the category and then hands the details to your jurisdiction.

In Arizona, that authority is the Department of Environmental Quality (ADEQ). So a builder here does not size a graywater system to a plumbing-code table. They build it to ADEQ's recycled water rules. That is the real content behind this section for a Valley home.

Arizona's Type 1 graywater permit

Most homes fall under ADEQ's Type 1 Recycled Water General Permit for Gray Water, written at A.A.C. R18-9-D701. It covers a private residence reusing less than 400 gallons of graywater a day. The permit is automatic. You file no application and pay no fee, as long as the system meets a set of best-practice conditions. The main ones:

• Keep the water on your own lot, contained inside the property line.
• Apply it below the surface or under a cover such as mulch. Drip and flood work; spraying does not.
• Avoid human contact with the graywater and with the soil it waters.
• Do not surface-apply graywater to food plants. Trees and shrubs are the exception, as long as the edible part never touches the water, which is what puts citrus and nut trees back on the list.
• Keep hazardous chemicals out of it, and do not store it, since standing graywater turns septic within about a day.

Above 400 gallons a day there is no Type 2 rung to step onto, because Arizona has no Type 2 general permit for graywater. Anything the Type 1 permit does not cover goes straight to the Type 3 Recycled Water General Permit at A.A.C. R18-9-D702, which reaches up to 3,000 gallons a day. Type 3 is a genuine filing: a Notice of Intent to ADEQ listing your graywater sources and showing the flow calculation, then written authorization back from the department before the system runs. A single-family home rarely gets close to 400 gallons a day, so Type 1 is almost always the path.

Plan it during rough-in

For example, a custom home in Cave Creek can send its laundry and shower drains to a separate graywater line that feeds a drip field under the desert trees, reusing hundreds of gallons a week. The catch is that this only works if the drain lines are split during the plumbing rough-in. Running a second set of stub-outs while the walls are open costs very little. Adding them after drywall means opening finished walls and a slab, which is expensive. If graywater interests you at all, decide before rough-in, which is the cheapest point in the whole build-on-your-lot timeline to build it in. In a climate where water is the scarcest thing on the lot, that reuse stretches a well or a city tap and carries a yard through the summer.

Which edition applies to your build

Graywater provisions have moved and been renumbered across recent codes, and the 2018, 2021, and 2024 editions organize on-site water reuse a little differently. The constant is that the IRC defers the working rules to the state, so in Arizona the ADEQ permit governs no matter which edition your city adopted. Confirm your city's edition in the building code editions by city reference.

Keeping the two water systems apart

A graywater line is part of the same drainage system that gets checked at your plumbing tests and inspection, and it runs alongside the potable water supply and pressure system without ever touching it. If you are still deciding how to plant the yard, weigh it against the options in artificial turf versus desert landscaping. The soil absorption section sits in Chapter 30 of the 2021 IRC.