General Water Quality Information

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Drinking Water Supply 

The drinking water in Tempe is produced at two water treatment plants. The Johnny G. Martinez Treatment Plant, dedicated and renamed after Johnny G. Martinez who was a City employee , in the Water Department. for 41+ years. The Johnny G. Martinez plant is in North Tempe near Papago Park. The other plant is simply named, the South Tempe Water Treatment Plant, as it's located in the southern part of the city.

Each plant receives surface water originating from various sources, including the Salt River, Verde River and Central Arizona Project (CAP, Colorado River) watersheds. The water is delivered via the Salt River Project (SRP) canal system. The Johnny G. Martinez plant is located on the X-cut canal, which receives water from SRP's Arizona canal. While the South plant is located on the Tempe canal, which receives water from SRP's South canal.

Additional water sources include SRP and Tempe wells. SRP has many wells located along the canal system throughout the valley. Tempe also has several wells, located throughout the city, that can pump chlorinated water directly to the distribution system. Tempe wells are pumped to the system when necessitated by water demand.

Changes in source water and various blends of the rivers are commonly experienced at the treatment plants. Salt River Project manages the water source blends and flows in the canals based on precipitation and watershed management conditions. The majority of water received at the treatment plants throughout the year is a mixture of the Salt and Verde rivers. 


The Salt River is characteristically higher in total dissolved solids (TDS) and chlorides (Cl-). While, the Verde River is higher in hardness(CaCO3). Fluctuations in water characteristics are dependent on the blends of source water being supplied to the plants for treatment. 


Disinfection of the water supply is accomplished by chlorination. Water leaving the treatment plants contains approximately 1 mg/L of free residual chlorine. The free chlorine residual continues to disinfect the water in the distribution system. Trihalomethanes, by-products of chlorination, are regulated by both the State of Arizona Department of Environmental Quality (ADEQ) and the US Environmental Protection Agency (EPA). Compliance testing for THM's in the distribution system is preformed quarterly, utilizing approved EPA methods. Tempe maintains THM levels which are below the maximum contaminant level (MCL), as established by the EPA. The MCL for THM's is currently 0.08 mg/l.

Presently, chlorination is the most widely-used method of disinfection in the water treatment industry. Research for alternative methods has produced effective disinfection techniques, but these methods produce disinfection by-products of their own. 


In Tempe, the naturally occurring fluoride in source waters is approximately 0.3 mg/L. This is supplemented to provide a finished water concentration for fluoride at 0.7 mg/L . This is considered by the American Dental Association (ADA) the optimum level of fluoridation and is most effective for prevention of dental caries in children up to their early teens. Research by the ADA has found that fluoridation preserves integrity of teeth into adulthood.

Supplementing the fluoride produces water considerably below the current EPA-established MCL of 4.0 mg/L. For additional information on fluoridation, contact the American Dental Association or seek advice from your dentist. 


The City of Tempe services approximately 160,000 people and is thereby required by the EPA to perform 120 microbiological tests per month on the water in the distribution system. Quality criteria for finished drinking water from public supplies is based on the presence or absence of total coliform, as stated in the Arizona Total Coliform Rule of 1991.

Tempe has it's own Water Quality Lab, certified through Arizona Department of Health Services(ADHS), which performs bacteriological analysis of coliform, implementing EPA-approved methods.

Testing is performed on treated water prior to entry into the distribution system and on water from representative sampling locations throughout the distribution system.

The City of Tempe consistently meets standards established for microbiology.


Seasonal occurrences of musty/moldy or earthy tastes and odors may be detected in the system water. Research, by laboratories dedicated to this subject, has determined the culprits are naturally occurring algal and fungal by-products. As algae in the canals die, compounds known as Methyl-Isoborneol (MIB) and Geosmin are released into the water. These stable complex compounds present in just parts per trillion are difficult to remove with current technology. The detection of these compounds is dependent upon an individual's olfactory sensitivity. Many people may never detect them, while others who are sensitive may detect the musty/moldy taste and smell at levels below instrument detection levels. Tempe uses activated carbon to adsorb the MIB and Geosmin, thus alleviating the taste and odor.

Tempe in conjunction with SRP, CAP and other valley cities, has participated in various studies to determine where the algae is most concentrated and the best way to control and alleviate the musty/moldy occurrence. A partnership with ASU is still under way which provides recommendations for treatment based on regular monitoring see the site for more information. The monitoring helps to determine the appropriate amount of carbon to feed in the plants to get the best tasting water possible.

Additionally, Tempe and SRP manage the canals and lakes to reduce the algal growth.

Research has determined that there are no indications of adverse health effects attributed to the water from these compounds.

Lead and Copper

Drinking water, leaving the treatment plants, is regularly tested and contains less than 0.002 mg/L lead and less than 0.05mg/L Copper. Therefore, the lead/copper levels in consumer taps most likely originates from home plumbing and not from municipal water systems. Water coming into contact with lead pipes, copper pipes with lead solder or other leaded materials may contribute to lead and copper in the drinking water. After an extended time of contact with consumer plumbing, lead and copper may leach from plumbing materials into the drinking water.

In the 1991 Lead and Copper Rule, the Environmental Protection Agency (EPA) required all public water systems to monitor lead and copper at residential taps. As a large water system serving greater than 100,000 people, Tempe was required to collect 100 lead and copper tap samples for two consecutive six month periods throughout the calendar year 1992.

The 1992, 2000, 2003, 2006 and 2009, 2012 and most recently in 2015 lead and copper test results indicated that Tempe is in compliance with the current EPA established action levels of 0.015 mg/l for lead and 1.3 mg/l for copper.

Since 1991, the EPA has made some changes to the Lead and Copper Rule. In complying with these changes, Tempe will collect and monitor samples from 50 homes built before 1935 or ones that were built after 1982 and before 1988, every three years (2018 is the next testing period). The testing is done only in homes built between these years. This is because the EPA has determined, they are the most likely to contain lead pipes, lead solder or copper pipes that have not yet "weathered" (acquired a protective mineral coating inside the pipes). Testing is the only way to determine if lead or copper are present.

Residents in Tempe concerned about lead or copper can take the following precautions to minimize leaching from the home plumbing.

Flush the water used for cooking and drinking from each cold water tap after the water has been standing in contact with your home plumbing for more than six hours (for example, overnight or during your workday). Flushing a tap for 1-2 minutes will insure that the water is representative of the water from the distribution mains and not from residential plumbing. Flushing is important because the longer water is exposed to the lead pipes or lead solder the greater the possibility of lead contamination. The flushed water can be collected and used for cleaning, on houseplants and gardens.

Never cook with or consume water from the hot water tap. Hot water dissolves lead more quickly than cold water. Use only water from the cold tap that has been thoroughly flushed for consumption.

The EPA also has more information about Lead on their website.

If you are planning to re-plumb your house or have any plumbing repaired, it is your responsibility to insure the use of low-lead materials, as required by this new law. Other environmental sources of lead are:

leaded paint
leaded gasoline
lead contaminated dust/soil
ceramic pitchers or plates with lead based glazes
leaded crystal
lead soldered seams of certain canned foods (acidic foods are especially susceptible to lead contamination)
brass and chrome plated faucet fixtures

The City of Tempe established a ban on the use of lead solder and lead pipes for construction in May of 1988.