Achieving safe yield, the fundamental objective of Arizona's 1980 Groundwater Management Act (GMA), may prove to be a more elusive goal than once expected. The GMA mandated that the Phoenix, Tucson and Prescott Active Management Areas (AMAs) achieve safe yield, a balancing of groundwater withdrawals with recharge, by the year 2025. Some of the assumptions and projections used to set the goal, however, have not held up after 20 years, with the result that safe yield may be a difficult target for some AMAs to reach.

A note of warning was sounded during recent Arizona Department of Water Resources (ADWR) efforts to draft third management plans for the AMAs. The draft plan for the Tucson AMA concludes that "given current projections, the AMA will not reach safe-yield by 2025." Estimates show that overdraft will still be 46,600 acre-feet per year. The draft plan for the Phoenix AMA shows potential overdraft of 372,932 acre-feet in 2025.

This concern has caused safe yield to become a topic for renewed discussion, with various questions now arising such as: How likely is it that Arizona's metropolitan areas will be at safe yield by 2025? If safe yield is not reached by 2025, can it be achieved later? Even if safe yield is reached in 2025, will population growth cause overdraft to resume shortly thereafter? How important is reaching safe yield, if overdraft is substantially reduced? Does ADWR need new regulatory tools to assure safe yield, or does the goal need to be redefined?

Meanwhile, it is becoming more evident how later developments threw off GMA water demand and supply projections. Unfortunately, from a water management perspective, nearly all such deviations have either increased water demand or slowed the switch from groundwater to renewable supplies. Both factors affect the ability to reach safe yield.

A critical determinant of water demand in the urban AMAs is population. Municipal water demand is the largest category of usage in the Tucson AMA and is second to agriculture in the Phoenix AMA. More importantly, it is the water demand component that is growing over time. As official population projections have been revised over the last two decades, the population forecast for Maricopa County in 2025 has continually been adjusted upward. Current projections show 4,948,423 Maricopa County residents by 2025. By contrast, population projections for Pima County have been revised downward, with the 2025 population pegged at 1,290,966.

Equally important is average municipal water demand, measured in gallons per capita per day (gpcd). In the 1980s, certain demographic trends seemed to guarantee significant reductions in gpcd rates. Conservation efforts were expected to yield further reductions. Existing residences were primarily single family homes, many with turf and pools, and most with evaporative coolers. By contrast, new housing was primarily multi-family rental units and townhouses with much less landscaping. Also, new construction favored refrigeration air conditioning over evaporative coolers.

These "trends" didn't last. An expanding economy and low interest rates have helped push home ownership rates to record levels, and reduced the number of apartments being built. Also, some of the apparent water savings among apartment dwellers proved to have been merely shifted off-site, to Laundromats and car washes.

New apartment complexes tend to be larger, have lusher landscaping, and offer more water-using amenities like pools, spas, gyms, garbage disposals and laundry facilities. Many new and existing single family residences have new water-using devices, such as outdoor misting systems. Pools, Jacuzzi, and whirlpool tubs continue to grow in popularity.

Water conservation has not lived up to its early promise in many areas. Significant reductions in gpcd rates occurred initially, as the easiest, most cost-effective measures were undertaken. But now conservation gains are coming harder, and some conservation devices lack durability. For example, many drip irrigation systems deteriorate after five to 10 years, as do some models of ultra-low-flush (ULF) toilets. The lack of available parts for repair and maintenance of some ULF toilets has forced many homeowners to simply use the toilet as is or replace with non-ULF parts, which can render the toilet a virtual water guzzler.

The human element has proven problematic as well. Studies now indicate that residents who irrigate their landscapes manually may be more water efficient than those using drip systems because the systems need to be well managed and carefully maintained to provide efficiency. The average homeowner, or the average landscape worker isn't doing either. Timers are not regularly being re-set, and systems are not being repaired and upgraded as needed and are therefore less efficient over time.

Swimming pool covers are used primarily in spring and fall to prolong the swim season, but not in summer when potential water savings are the greatest, because a covered pool becomes too warm for comfort.

Another prediction that hasn't borne out was that municipal water rates would rise significantly faster than the inflation rate, providing a financial incentive to conserve. While rates have gone up in some areas, rates in other areas, such as Tucson, have actually gone up more slowly than overall inflation, thereby reducing the real price of water. Also, incomes have risen, making people less sensitive to the price of water. In addition, with refrigeration largely replacing evaporative cooling in new residences, summer electric bills now may be so much higher than water bills that the latter may not seem excessive.

Water demand in non-municipal sectors likewise has deviated from expectations. In the 1980s, Arizona copper mines appeared unable to compete with foreign companies, which had the advantage of cheaper labor, higher grade ore bodies and fewer environmental restrictions. Copper mining was viewed as a temporary activity, likely to disappear as early as the year 2000, as existing ore bodies played out or became uneconomical to mine. Thus, copper mines were granted the right to pump groundwater without much restriction.

Instead, copper mining in Arizona has rebounded with a vengeance, aggressively utilizing new technologies to efficiently extract more copper from lower-grade ore. Today, eight new copper mines or major expansions to existing mines are planned in Arizona, with several of them sited in the Tucson and Pinal AMAs.

Also agricultural water demand was projected to decline over time as irrigation efficiencies increased and farmland on the urban fringe was urbanized. What agriculture remained was projected to switch from pumped groundwater to Central Arizona Project (CAP) water.

Many agricultural irrigators however are finding it difficult or impossible to achieve 85 percent irrigation efficiencies. Agricultural lands have been largely urbanized in some areas, but in other areas, including the Tucson AMA, much development remains concentrated in the foothills, not in the flatter, agricultural portions of the AMA. Incentives to steer development toward agricultural lands or buy out farmers have not been put into place.

As water demand has remained stubbornly high, efforts to switch to renewable supplies have encountered unexpected difficulties. Cities were expected to accept and directly deliver large quantities of CAP water, with farmers and irrigation districts taking the rest. But CAP water has proven too expensive for many irrigators, who continue to pump groundwater.

CAP usage has failed to meet expectations in other areas, too. The City of Tucson, which holds the largest single municipal contract, treated and delivered CAP water for only a short period, when a combination of acidic water and aging water mains produced corrosion problems and brown water at the tap. The treatment plant was shut down, and the community continues to debate how best to use its CAP allocation. Copper mines remain leery of using CAP water because of its fluctuating water quality, and in some cases, fear that a cessation of groundwater pumping could cause localized chemical plumes to spread through the aquifer.

Use of effluent has increased enormously since 1980, but a 1989 court decision that concluded it was neither surface water nor groundwater has reduced ADWR's ability to regulate its use. The biggest category of effluent use is turf irrigation. While a growing number of new and existing golf courses and other large turf facilities now use reclaimed water, many still are built and, at least initially, irrigated with groundwater.

Ironically, most of the developments that have made safe yield a more difficult goal to achieve are good news when not viewed from the narrow perspective of a water resource manager. More affordable housing, a profitable copper industry, relatively cheap water, and a state economy that continues to attract new business and people in huge numbers all add up to a rosy economic scenario. Conversely, this makes the increased water demands associated with prosperity more difficult to attack.

That safe yield might not be reachable by 2025 has long been acknowledged. The state auditor general in 1989 stated that the AMAs might not achieve safe yield by 2025, and recommended the Legislature convene a groundwater code study commission. ADWR director Bill Plummer disagreed, stating that safe yield was still achievable under the existing code, and opining that such a study "could generate divisive attempts to alter the basic structure of the Code which, the draft report finds, has served Arizona so well."

Nine years later, fears of re-opening the code remain, and water demands continue to deviate from earlier projections. While the fate of the safe yield goal is far from clear, the issue appears to be moving to the forefront.