Colorado River cuts put Arizona’s well-pumping limits back in focus

Colorado River cuts can push Arizona farms toward groundwater, but a lost river allocation does not translate automatically into an equal volume pumped from wells. The replacement depends on groundwater rights, well yield, equipment condition and the cost of lifting water to the irrigation system.

For pump owners and maintainers, the practical question is not simply whether an old well can run again. It is whether that well can deliver the required flow at today’s pumping water level, for enough hours to cover the shortfall.

What the 2027–2028 cuts mean

As of October 30, 2026, the federal 2027–2028 operating guidelines provide for 1.25 million acre-feet of annual reductions in Lower Basin Colorado River deliveries in each of those two years. The Interior Department lists Arizona’s share as 760,000 acre-feet per year if the Lower Basin states implement their proposed sharing agreement. That condition matters: the statewide figure is not a groundwater-pumping target or a farm-by-farm allocation. Interior’s announcement and Reclamation’s release describe the same operating framework.

The impact differs by location and water entitlement. In September 2026, Cronkite News reported that Yuma-area farms’ senior rights protected them from immediate cuts, while most farms in the Central Arizona Project’s agricultural pool had already lost that supply. Some central Arizona farms still obtain CAP water through other arrangements. The new statewide reduction therefore does not mean every Arizona farmer faces a new, identical irrigation shortfall. Cronkite News

Groundwater replacement is already happening—but not everywhere

In its March 2026 coverage, High Country News reported that the irrigation district serving Pinal County farm manager Will Clemens drilled a dozen new wells after river deliveries were cut in 2022. It also described incomplete irrigation and difficulty keeping up with farmers’ water orders despite the additional wells. That is evidence of a local response, not a measurement of statewide pumping growth. High Country News

A different situation faces Brian Wong of BKW Farms in Marana, northwest of Tucson. Cronkite News reported that his farm could obtain CAP water through 2027, but its wells had been unused for about 30 years. Restarting them would require well refurbishment and changes to the irrigation system. Wong said he would reconsider cropping patterns and possibly leave acreage unplanted before taking those steps. Cronkite News

These examples show two distinct jobs: adding groundwater capacity to an operating district, and evaluating a dormant well system. Neither is just a motor replacement.

Falling water levels change the pump’s job

A well pump must overcome total dynamic head: the lift from the pumping water level to the delivery point, plus required delivery pressure and friction losses through piping, fittings and equipment. NDSU Extension’s irrigation pump guidance explains these components; velocity head is usually negligible in irrigation calculations.

Use the water level while pumping at the intended rate, not just the standing water level or the drilled depth. A deeper borehole does not by itself establish either available flow or required lift. NDSU’s well-performance guidance distinguishes static water level from pumping water level and explains how drawdown affects well performance.

As groundwater levels fall, the lift increases. The USGS identifies higher pumping costs, potentially declining well yield and possible needs to lower pumps, deepen wells or drill replacements among the consequences of groundwater depletion. USGS

For scale, an illustrative system delivering 1,000 gallons per minute against an additional 100 feet of head would require about 27 kW of additional electrical input, assuming unchanged 70% overall pump-and-motor efficiency. This is calculated from the water-horsepower and efficiency equations in Oklahoma State University’s pump-testing guidance, not a measured Arizona operating cost. Actual consumption depends on the pump’s performance at the new operating point.

A larger motor alone does not establish that the well can supply more water.

Before restarting or upsizing an irrigation well

Resolve these checks before committing to equipment:

• Withdrawal authority: Confirm the land’s groundwater entitlement and applicable management-area requirements with the Arizona Department of Water Resources. Within an Active Management Area, withdrawing groundwater from a well with maximum pump capacity above 35 GPM requires a groundwater right or permit; most such withdrawals also require measurement and reporting. The exemption for smaller pumps generally applies to non-irrigation use, not unrestricted farm irrigation. ADWR’s AMA guidance
• Work authorization: Check the requirements for drilling, deepening, replacing or modifying the well. ADWR provides different application and notice forms depending on the work and location. ADWR well forms
• Current well performance: Have a qualified contractor measure flow, pumping water level, drawdown and recovery. Do not size a replacement from a decades-old output figure alone. Keep the results as a baseline for later comparisons. Well-performance guidance
• Complete-system condition: Inspect the pump, motor, electrical supply, controls and discharge piping. Compare measured flow, head and power input with the relevant pump curve rather than relying on nameplate horsepower. Pump-system testing guidance
• Seasonal duty: Calculate the missing irrigation volume and the hours available to deliver it. Include rehabilitation, energy and distribution-system changes in the comparison with reduced irrigated acreage or changed cropping patterns.

If well water will feed a pressurized irrigation network, evaluate lift and distribution pressure together; our irrigation booster-pump sizing guide covers the flow-and-head selection step.