By Nathan, Sell My Land Arizona · Updated October 29, 2026
What a perc test measures and who runs it
A percolation test measures how fast water drains through the soil at the spot where a septic drain field would go. Someone digs a hole, fills it, and times how many minutes it takes the water to drop an inch. The county or the state's wastewater program uses that number, along with soil characteristics and how deep the ground is to rock or groundwater, to decide what kind of system the lot can have.
In Arizona the state rule that turns the test into a design number is A.A.C. R18-9-A312. It converts a percolation rate between 1 and 120 minutes per inch into a soil absorption rate, and it says a rate faster than 1 minute per inch or slower than 120 requires a site-specific rate set by the engineer. Where two methods, such as the soil evaluation and the perc test, give different numbers, the lower one controls. So "failed" can mean the soil is too slow, too fast, too shallow over rock, or too close to groundwater for the standard design. It does not mean the land cannot ever have a wastewater system.
Who reviews the application depends on the county. The Arizona Department of Environmental Quality holds the authority for septic permits and has delegated it to the counties, so a seller usually starts with the county's environmental office, and what a county handles can differ. Santa Cruz County's septic page, for example, says the county handles conventional septic permits and that other permits go to ADEQ directly. Call the county that covers your parcel before you assume which office applies.
What Arizona's rules give you instead
The same rule set, in R18-9-E301 through E320, lists the state's general permits for on-site systems. The standard one is 4.02, a septic tank with a trench, bed, chamber or seepage pit. There are many others. They include a composting toilet, two kinds of evapotranspiration bed, a Wisconsin mound, an engineered pad, sand, peat and textile filters, an aerobic system, a constructed wetland, and a sewage vault, which is a sealed tank that is pumped out instead of draining into the ground.
Each has its own conditions, and the engineer, the county or ADEQ decides which one fits a given lot. A mound or an engineered pad can handle soil that is too tight; a vault or composting toilet takes the drain field out of the picture. What each costs depends on the system and the site, so ask a licensed installer and your county for written figures before you decide what the lot is worth to you.
How much less failed-perc lots have sold for
We looked for lots whose listing text says the test failed. Of 33,906 vacant lots that sold in Arizona from October 2024 through August 2026, 15 say so in plain words, and every one is a small subdivision lot in two places: Show Low and Rio Rico.
In Rio Rico, 9 failed-perc lots sold, typically on about three-quarters of an acre. Their median price was about 38 percent below the median for the 511 other Rio Rico lots of 0.2 to 2.6 acres. Eight Rio Rico lots whose text says the test passed sold for a median more than double that of the failed-perc lots.
In Show Low, 6 failed-perc lots sold, mostly quarter-acre lots, and their median price was less than a fifth of the median for the other 465 Show Low lots of 0.2 to 2.6 acres. That comparison is not clean: the failed-perc lots are small, in specific neighborhoods, and the rest include larger and better-served lots. Read it as "much cheaper," not as a discount percentage.
Fifteen sales is a small sample. What it does show is that these lots sell, to buyers who read "will not pass perc" in the listing and still paid something. It also shows what listings do not say: only 481 of 23,994 sold-listing descriptions mention a perc test at all, so most buyers are not told either way. The land value lookup shows what each size band of Arizona land has sold for, which is the starting point before the failed test is taken into account.
