Introduction

There are over 93,000 domestic use wells in Arizona.  These private wells provide water to an estimated 120,000 households, with some 300,000 persons, or about 5% of the state’s population.  About 10-30% of the U.S. population depends on domestic wells for their water (Bartholomay, et al., 2007).  Information about the total number of domestic wells in the U.S. is difficult to obtain,  but according to the Center for Disease Control more than 90,000 new wells were installed in the U.S. in 1998 (CDC, 1998). In Arizona the number of new domestic wells now exceeds 3,000 each year (ADWR,  2008).  The U.S. EPA (2008) reports that “approximately 15% of Americans rely on their own well...” for water.  But domestic well waters are not subject to EPA drinking water regulations, and undergo no governmental quality tests for potability in Arizona (note: New Jersey is one of the few states requiring domestic wells be tested with any real estate property transaction).

Well owners are not trained as well operators and are often unfamiliar with water quality standards and testing, and rarely know much about their systems or the local aquifer.  A recent nationwide survey of well water quality conducted by the U.S. Geological Survey indicates that about 79% of the wells (12,318 of 15,495 tested) contained one or more contaminants that may be harmful to human health. Of those wells sampled, about 9-11% had arsenic and nitrate levels exceeding the U.S. EPA maximum contaminant levels (MCLs) established for drinking water standards.  Also, less than 1% of the wells had organic contaminants like the herbicide atrazine above drinking water standards (Focazio, et al., 2006).  Radon-222 gas, presently not regulated by the EPA, was detected in 98% of the wells sampled.

A recent well water quality study of a small number of wells from seven Arizona counties found that  about 90% of the wells exceeded at least one contaminant standard (such as nitrates, arsenic, and/or coliforms). For example, 43% of domestic well waters sampled are contaminated with waterborne pathogens, and 33% of the wells had nitrate or arsenic levels exceeding the EPA standards (Karpiscak et al., 2006).  The data from these recent surveys suggest that domestic well owners should regularly monitor their well water quality. They should also consider home water treatment systems to bring their well water quality to national drinking water standards.  

This Well Owner’s Guide presents detailed sections that assist the reader to become familiar with water quality concepts, drinking water guidelines, well system operation and maintenance, and water testing.  The reader is also introduced to Arizona’s aquifers, as well as conditions and activities that effect ground water quality.  Well owners can also learn about well construction, well components, and well maintenance needed for the safe and proper function of their wells. Finally, a section on water treatment technologies based on water quality conditions is presented.

Arizona Water Sources

The total amount of water that circulates annually from the earth’s surface to the atmosphere and back down to the earth has remained fairly constant.  On average, rivers and lakes produce the same amount of fresh water now as they did 100 years ago. However, the population of the world has increased more than six-fold in the last 100 years, increasing demands on fresh water resources.

Although ground water is considered a renewable resource in regions with plentiful rain and snow, it is considered a non-renewable resource in the arid West and many other parts of the U.S. and the world where pumping exceeds recharge in many aquifers.

There is insufficient rainfall in Arizona’s dry climate to recharge the aquifers and to keep pace with increased pumping, resulting in many of our aquifers in significant overdraft.  Ground water in the Tucson basin has been age-dated to be between 300 and 8,000 years old.  In the San Pedro River basin, the ground water has been age-dated to over 12,000 years old. Age-dating estimates the time elapsed since the water fell as rain or snow before it percolated to the ground water. 

Where ground water is near the land surface and discharges to a river bed, perennial rivers occur. During rainfall events, this ground water ‘base flow’ is mixed with rainfall runoff.  For example, after the summer monsoons, water flowing in the San Pedro River has been age-dated and found to consist of a combination of ground water and recent rainfall.

Figure 1: Arizona water supplies

Growth in the arid southwest United States is sustained by the use of mostly ground water and river-fed reservoirs. Presently, about 44% of Arizona’s water supply come from in-state ground water sources, as shown on Figure 1. The water supply reservoirs contain a mixture of water derived from seasonal snow melt, rainwater, and ground water base flow.  Surface water from in-state rivers and reservoirs meets about 14% of Arizona’s water needs.

Arizona also has an annual allocation of 2.8 million acre-feet of Colorado River water, established by a Federal Supreme Court decision in 1964, which accounts for nearly 40% of Arizona’s total water supply. Following a 1973 Supreme Count Decision, the Central Arizona Project (CAP) began construction of a canal to deliver Colorado River water across the state. Today, CAP water accounts for about 21% of the state’s water use. Reclaimed water meets about 2% of Arizona’s water demand. 

Although CAP water is a dependable resource, Arizona’s allocation of Colorado River water is limited by Federal law and access to it is constrained by proximity to the canal.  Because of our ‘junior’ water right to the Colorado River, Arizona’s allocation of CAP water will be the first to be reduced in a regional drought. 

Agriculture remains the primary user of water resources in Arizona accounting for about 74% of the  7 million acre-feet of water used annually during 2001-2003. (ADWR, 2008). 

The Arizona Ground Water Management Act (Title 45 of the Arizona Revised Statutes) was passed in 1980 to conserve, protect, and allocate ground water resources and provide a framework for management and regulation.  The Act has three primary goals:

• Control the severe ground water overdraft occurring in many parts of the state;
• Provide a means to allocate the state’s limited ground water resources to most effectively meet the changing needs of the state; and,
• Augment Arizona’s ground water through water supply development.

Figure 2: Arizona active management areas

To accomplish these goals, the Act established the Arizona Department of Water Resources (ADWR) to administer the Act’s provisions. “Active Management Areas” or “AMAs,” were established across the state (Figure 2) to manage excessive pumping. Most of the AMAs have established a goal of “safe yield” by the year 2025. “Safe yield” would be achieved when the volume of ground water extracted does not exceed the volume of ground water recharging the system. Excessive pumping was found to result in land subsidence as the water table drops. Also, water pumping costs and mineral content (total dissolved solids— TDS) increase with aquifer depth.

The Arizona Ground Water Management Act of 1980 identifies wells used for domestic or household purposes as "exempt wells" because owners aren’t required to report to how much water they pump.  Owners of exempt wells are permitted to pump no more than 35 gallons a minute, or 18.4 million gallons a year. However, as the number of exempt wells increase in the AMAs, the accumulated volume of unregulated extraction is causing concern.   It is expected that future regulations may require monitoring of exempt well pumpage so as to manage safe yield goals.