The highest-quality water on the lot, free, daily, all summer.

What it is

Every air-conditioning system that cools indoor air below the dew point produces liquid water at the evaporator coil. That water is collected in a drain pan and routed, by code, to a primary condensate drain — typically a 3/4″ PVC pipe — which exits the building at the air handler. In most Tucson homes, the line dumps onto a stucco wall or a sidewalk, where the water evaporates within minutes. COND-1 intercepts the line at the building exit, routes it into a 1/2″ PEX line, and delivers the water to the root zone of a tree.

The water is exceptional. It is distilled (no minerals, no chloride, no sodium), cool (5–10°F below ambient), and constant during the long Tucson cooling season. A typical 4-ton residential split-system in Tucson runs about ten hours a day in July and August and produces between 1.2 and 2.0 gallons per ton-hour, depending on indoor humidity and outdoor dew point. The arithmetic is on the next section. The point is that this is forty days of free, exquisite irrigation and the only reason most houses don't have it is that no one ran the line.

The condensate math

Daily condensate yield (gal) ≈ tons × runtime hours × W, where W is a humidity-dependent constant that ranges from 0.6 (dry, dew point below 35°F) to 2.5 (wet, dew point above 65°F). For a Tucson 4-ton system running 10 hours/day during monsoon (dew point typically 50–62°F), yield runs 12–20 gal/day. Across a 120-day cooling season, total yield averages ~1,400 gal — comparable to running an outdoor faucet for two hours every day at 6 gpm. Across the entire summer, on a small lot with a single shade tree, this is enough water to keep that tree alive without any other irrigation.

The University of Arizona Water Resources Research Center has published a 2014 study measuring residential AC condensate at typical Tucson dew points and finding sustained outputs of 14 gallons per day on 3-ton systems. We've measured similar numbers on our own meters across 109 active COND-1 sites.

Schematic

Bill of materials, typical 4-ton install

The above is the most common COND-1 build. A two-handler home with a split between upstairs and down runs about $850; a more elaborate run with longer pipe and multiple receiving plants tops out around $1,800. We've never billed more than that for a COND-1 build in eight years.

Maintenance & concerns

Three failure modes occur, all of them rare and all of them easy to fix.

P-trap clog. Indoor coils shed dust, dust mixed with condensate sludges in the trap, the line backs up, and on most modern systems a float switch in the secondary pan trips the AC and shuts it off. The fix is a wet-vac applied at the line termination outdoors, or a mild bleach flush quarterly during summer. We include a one-page maintenance card with every install.

Freeze. Tucson sees roughly four to seven nights per winter below 28°F. The 1/2″ PEX line is freeze-tolerant down to 20°F if it has a complete fall and no low points; if not, it'll split. We design every line with a continuous fall and use UV-jacketed PEX-A rather than -B (better freeze ductility).

Excess water at the basin. A 4-ton system running fully through monsoon will deliver more water than a young tree can use. We size the receiving basin large enough to handle 25 gal/day and we always overflow it onto an EARTH-1 swale or basin uphill of any other tree. Over-watering is the rare problem of having the right amount of water in the wrong place.