Responsible Management of Our Water

The figure cited at the September council meeting, a 14 percent faster decline, is accurate. The deep aquifer dropped an average of 0.69 feet a year from 2013 to 2017 and 0.80 feet a year from 2019 to 2023, and PBAC printed both on a single slide in February 2026. The question is what changed between those two periods.

The same presentation explains the change. Moscow once drew about a third of its supply from the shallow Wanapum aquifer. In 2017 and 2018 the city stopped, because that water requires iron and manganese filtration and the filters waste a meaningful share of what they treat. Moscow's shallow-aquifer pumping fell from an average of 253 million gallons a year to 7, while its deep-aquifer pumping rose from 581 to 773. The difference, about 192 million gallons a year, is water the city was already using. It now comes from a different aquifer.

PBAC's technical manager described the effect in February 2026: "by cutting themselves out of the upper aquifer, they've added a new Palouse and UI to the lower aquifer." The town of Palouse, Washington and the University of Idaho together pump roughly 190 million gallons a year, so the shift added the equivalent of both to the deep aquifer's load. The shallow aquifer has been recovering since.

A common assumption in Moscow is that roofs and parking lots keep rain from reaching the aquifer, so that every new building means less water underground. John Bush, the geologist whose maps of the basin PBAC adopted, has addressed that assumption with records going back to 1925.

His conclusion is that the shallow aquifer under Moscow receives about 400 to 500 million gallons of new water a year, and that four separate calculations over the past century arrive at roughly the same figure. At the November 2022 meeting he said: "recharge calculations have been repeated by four different people it's about the same number." In his recorded lecture on the upper aquifer he put it this way: the capacity "hasn't changed even with all the development, the blacktop."

Where that water enters the ground is still debated. Bush's lectures place it along the mountain front east of town, moving laterally through buried sand channels. A 2006 drilling study he co-authored with Mark Solomon for the state found little evidence for that route and pointed instead toward the area near the state line, west of town. On the point that matters here, the two agree: a thick layer of clay and basalt beneath the city blocks the downward path, so whether a given lot in town is lawn or parking lot has no bearing on what reaches the aquifer.

Since the groundwater plan took effect in 1992, Moscow's population has grown 42 percent and Pullman's 49 percent. Over the same period, combined pumping by Moscow and the University of Idaho fell 18.9 percent, and combined pumping by Pullman and Washington State University fell 7.6 percent. These are PBAC's figures, published in its 2025 annual report.

Per person, the decline is larger still. PBAC's February 2026 presentation puts per capita pumping down 47 percent for Moscow and UI and 38 percent for Pullman and WSU. The region added residents and used less water in total.

One caveat: each city shares a water system with its university, so a city-only figure is, in the technical manager's words, "a false number." The figures above are the paired totals PBAC itself uses.

The figure originates in the 1992 Ground Water Management Plan, where Moscow's action plan set a target of 125 percent of its 1981 to 1985 average pumping. The plan's language is "attempt to limit." PBAC's 2015 update describes the standards as "voluntary (1% annual increase and 125% ceiling) standards."

It has never functioned as a cap. PBAC's own charts show Moscow above 875 in eight years between 1994 and 2015, and PBAC's 2000 annual report noted the exceedances at the time. Pullman adopted a separate ceiling of 959 million gallons in 2021. Neither city faced state action.

PBAC's vice chair explained the plan's purpose in January 2023: the entities cooperated "in order to fend off getting declared a critical groundwater management area." That designation would transfer decisions about how much Moscow may pump from the city to the State of Idaho. PBAC's technical manager went further the following month and called the targets "based upon a groundwater model that was flawed."

The state has already ruled on this question. In November 2003, five groups petitioned the Idaho Department of Water Resources to declare the Moscow area a critical ground water area, halt new water rights, and cut pumping by priority. On December 1, 2004 the Director denied every request and ordered only an annual review of water levels and of PBAC's plan. When the petitioners sought reconsideration, he denied that as well, on January 4, 2005, writing: "The Director recognizes that individual entities have exceeded some Palouse Basin Aquifer Committee (\"PBAC\") goals. However, from a basin-wide resource perspective, stabilization of pumping from the Grand Ronde aquifer system has occurred, indicating that the voluntary nature of the management strategies has thus far been effective." Neither order places a pumping limit on the City of Moscow, and the 875 figure appears in neither.

Moscow pumped 845 million gallons in 2025, close to the goal. The goal remains what it has always been: a committee target, derived from a model PBAC no longer relies on, that both cities have exceeded before.

The council was told that the city's 425 undeveloped residential lots, fully built out, would add 76 million gallons a year to demand. Later in the same meeting the estimate rose to 490 lots and 85 million gallons. Either figure is worth setting beside the shallow aquifer Moscow stopped using.

PBAC's February 2026 presentation estimates the safe yield of the shallow aquifer at Moscow's east-side wells at 170 million gallons a year. Safe yield is the volume that can be pumped indefinitely without the water level falling. The estimate rests on a simple observation: between 2004 and 2026 the water level in that aquifer ended where it started, and over those 259 months the city pumped 3.67 billion gallons from it, which works out to about 170 million a year. It is an estimate, and PBAC presents it as one. The committee discussed restarting those wells at its May and August 2026 meetings.

The shallow aquifer has been recovering since 2017. PBAC's technical manager described the monitoring well at the old police station as "recharging and going back to the levels that it used to be before it was pumped." The water is available. Using it again means paying to filter it.

When PBAC studied a supplemental water supply in 2017, it had to define how much less pumping would hold water levels steady. It set that figure at 735 million gallons a year and defined it as "current or baseline irrigation demand." In other words, the volume that would stop the decline is roughly the volume the region puts on lawns and fields each summer.

From November through April the basin pumps about 6 percent of its annual total each month. In July and August the figure is 15 percent. PBAC's 2022 report found that July through September alone accounted for 43 percent of the year's pumping, and that without outdoor use those months "would have used roughly 18.9%."

The connection to housing is direct. A home on a small lot uses less water per person than a home on a large one, because the lot is what gets irrigated. Zoning that requires larger lots requires more irrigation.

Two quantities are measured in this basin: water levels, recorded hourly in about 34 monitoring wells since 2006, and pumping, reported monthly by each city and university since 1992. Everything else is an estimate.

Recharge, the rate at which the aquifer refills, has been estimated at least 24 times since 1923, in five different units, without agreement. A 2009 University of Idaho thesis that compared twelve of those studies concluded that "there is no consensus on the amount of recharge." A 2015 paper by two UI geophysicists stated: "The first order unknown is recharge."

This is a long-standing gap. When the state reviewed the aquifer in 2004 it found that "Available information is also inadequate to determine that water use exceeds the reasonably anticipated average rate of future natural recharge in the lower aquifer." The same year, the University of Idaho hydrogeologist who briefed the Idaho Legislature on the basin wrote: "Does this aquifer receive recharge? Yes," and then: "we do not know if the recharge rate is greater than or less than the combined pumping rate of the four entities." Twenty-two years later that remains the state of knowledge. PBAC has never published an estimate of how much water the aquifer holds, and no model exists that can forecast future levels. PBAC's technical staff said in 2022 that the current model is "not going to be valuable from a predictive standpoint" and that building a real one would take "a lot of money drilling holes."

Nothing in the record says when a pump would run dry, or whether one would. The decline is real and its rate is well measured. How long the supply lasts is unknown, because the size of the supply has never been measured.

The geology is not in dispute. John Bush, whose maps of the basin PBAC uses, spent 2024 re-reading more than 150 drillers' logs from the granite foothills. His conclusion, from an October 2024 PBAC session: "when you get into real granite, low yield wells, they're probably mostly coming from soft zones and fractures," and, citing the long-held view of hydrogeologist Dale Ralston, "once they're into hard granite, they're probably not connected to the aquifers down in Moscow." Bush himself thinks there is a slow connection through a maze of sediments, but on the point that matters he was direct: "I think they're connected but they're not the same water levels ... every one of these wells water level is like 15, 20 feet from the top of the well." Moscow's water, he noted, sits more than two hundred feet down.

Dry foothills wells in dry summers are an old condition. A 2007 University of Idaho thesis in PBAC's library recorded it before any of the subdivisions now being debated existed: "Area residents are concerned in drier years because some domestic wells have gone dry by the end of the five-month dry season due to decline of the water table." A low-yield well in granite drains in a dry season whether or not anyone builds a house in town.

In 2025 the University of Idaho began sampling private wells on the Moscow Mountain apron east of Highway 95 for PBAC, to trace where recharge enters the aquifer. Ten wells had been sampled by the September 18, 2025 PBAC meeting (report at 7:44) and nineteen by the November 20, 2025 meeting (report at 33:49). Both reports to the committee are recorded and linked in source 27. They discuss well counts, owner contact, and early results. Neither reports a well as dry.