No filters. No pumps. No tanks.

What it is

GWY-1 is the simplest and most-installed subsystem we run. We tap into your washing-machine drain hose or your shower drain, route the water through a brass three-way diverter (so you can switch back to sewer for a heavy bleach load), and gravity-feed it to mulched basins around your trees through 1-inch black HDPE drain pipe. There are no filters because filters clog. There are no pumps because pumps fail. There are no holding tanks because greywater is required by law to be applied within 24 hours of generation, which gravity guarantees.

The system is named "branched drain" because the supply pipe branches at predetermined splits using straight-through-and-side-outlet fittings — water finds its level among the basins by passive flow. The technique is described in detail in Art Ludwig's "Create an Oasis with Greywater" and codified in part in Tucson's 2008 stub-out ordinance, which requires new residential construction in the city to include a greywater stub-out near the washing-machine standpipe whether or not the homeowner is using it yet.

Legal status in Arizona

Arizona is one of the easiest greywater states in the country. The ADEQ Type 1 Reclaimed Water General Permit covers private residential reuse under 400 gallons per day at no fee, with no inspection required, provided the system meets thirteen conditions enumerated in Arizona Administrative Code R18-9-711. Among the conditions: human contact is avoided, water is contained on the property, no surface application on food crops other than citrus and nut trees, no standing water on the surface, the system has a clearly marked label, and the homeowner has notified the local jurisdiction (in Tucson, that's Pima County's Gray Water Reuse program).

We file the Type 1 declaration on every greywater install we do, even though it's free and self-administered, because the paperwork is the difference between a system the next owner of the house can keep using and a system they have to rip out at sale. Pima County's two-page pamphlet is the cleanest plain-English summary; we hand a copy to every greywater client.

Schematic

Sources of greywater on a Tucson home

Greywater is, by Arizona definition, "wastewater collected separately from a sewage flow that originates from a clothes washer, bathtub, shower, or sink, but does not include wastewater from kitchen sinks, dishwashers, or toilets." A typical Tucson household generates the following volumes (Tucson Water residential usage data, 2024):

• Washing machine: 14–25 gal/load × 4–7 loads/wk = 56–175 gal/wk
• Showers: 18–25 gal/shower × 14 showers/wk = 250–350 gal/wk
• Bathroom sinks: 20–40 gal/wk per bathroom
• Bathtub fills (occasional): 35–50 gal/event

The total typically falls between 350 and 600 gal/wk, far under the 400 gpd permit ceiling for a single residential household. We almost always start with the washer (the easiest tap) and add showers in a second visit if the homeowner wants more capacity.

Bill of materials, typical laundry-to-landscape install

Soaps that work, soaps that don't

The biggest mistake new greywater users make is sending salt-loaded detergent into the system. Sodium kills mesquites and citrus on a slow timeline, and most mainstream powders and many liquid detergents are heavy on sodium-based brighteners. We hand every client a one-page sheet (we'll mail it on request) listing the four detergents we recommend: Oasis Biocompatible (the gold standard), Ecover liquid, Bio Pac liquid, and Dr. Bronner's Sal Suds at 1 oz/load. The detergent change is non-negotiable; the rest of the install is wasted if the trees die from chloride buildup.

What we won't do

We will not run greywater from a kitchen sink — Arizona law explicitly excludes it from the Type 1 permit, and grease loads make a basin go anaerobic in a single summer. We will not run greywater into vegetable beds (food-crop surface application is not permitted under Type 1, except citrus and nuts). We will not install a pumped greywater system with filtration and storage; that is somebody else's specialty. We will not connect greywater to a system with rainwater overflow that crosses the same outlet, because that overflow path can mix sources and is harder to label and maintain.