Maximum Contaminant Levels

Regulated Drinking Water MCLs or Alert Levels

Stage 2 Disinfection By-Products: Haloacetic Acids (5) MCL

Sum of monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic Acid, and dibromoacetic acid: 0.060 mg/L.

If monitoring quarterly, compliance with the MCL is based on the locational running annual average of data from the most recent four quarters. If monitoring annually or less, compliance is based on the current result.

Inorganic Chemical MCLs

Antimony: 0.006 mg/L
Arsenic: 0.010 mg/L (effective 1/23/06)
Asbestos: 7 MFL
Barium: 2 mg/L
Beryllium: 0.004 mg/L
Cadmium: 0.005 mg/L
Chromium: Total: 0.1 mg/L
Cyanide: 0.2 mg/L
Fluoride: 4.0 mg/L (2.0 mg/L SMCL)
Mercury: 0.002 mg/L
Nickel: None
Nitrate: 10 mg/L
Nitrite: 1 mg/L
Selenium: 0.05 mg/L
Thallium: 0.002 mg/L
Sodium: None

Compliance with the MCL is based on the running annual average.

Lead and Copper Alert Levels

Lead Alert Level: 15 ug/L
Copper Alert Level: 1.3 mg/L

Compliance with the Alert Level is based on the 90th percentile.

Maximum Residual Disinfection Level

Chlorine: 4.0 mg/L

Compliance with the MCL is based on the annual average of the monthly averages for the previous 12 months.

Radiochemical MCLs

Gross Alpha or Adjusted Gross Alpha Particle Activity: 15 pCi/L
Combined Radium (Radium-226 and Radium-228): 5 pCi/L
Uranium 30 ug/L

Compliance with the MCL is based on the running annual average.

Synthetic Organic Chemical MCLs

The MCLs for the 36 SOCs are listed in the SOC MCL Table.

Compliance with the MCL is based on the running annual average.

Total Coliform MCL

Compliance with the MCL is based on the presence or absence of coliforms. For a system which collects at least 40 samples per month, no more than 5% of the samples collected in a month can be total coliform-positive. For a system which collects fewer than 40 samples per month, no more than one sample collected during a month is total coliform-positive.

Fecal Coliform MCL

Any fecal coliform-positive repeat sample or E. coli-positive repeat sample, or any total coliform-positive repeat sample following a fecal coliform-positive or E. Coli-positive routine sample.

Stage 2 Disinfection By-Products: Total Trihalomethanes MCL

Sum of bromoform chloroform, bromodichloromethane, and chlorodibromomethane: 0.080 mg/L.

Compliance with the MCL is based on the locational running annual average of data from the most recent four quarters. If monitoring annually or less, compliance is based on the current result.

Volatile Organic Chemical MCLs

The MCLS for the 21 regulated VOCs are listed in the VOC MCL Table.

Compliance with the MCL is based on the running annual average.

What are the sources of contaminants in drinking water?

The Sources of Contaminant in Drinking Water Table lists sources of contaminants in drinking water. It was derived from the EPA's Drinking Water Contaminants web page.

How often are Tucson Water sources tested to comply with the Drinking Water Regulations?

Monitoring requirements, including frequencies and locations, are specified within the drinking water regulations. In general, monitoring is required at the distribution system or at the Entry-Point-to-the-Distribution-System (EPDS).

The monitoring frequencies are dependent on the results of the previous sampling events. More frequent monitoring is implemented when a level approaches the MCL in order to make the necessary adjustments to prevent an exceedance, including shutting the well down. With ADEQ approval, a monitoring reduction is used when a contaminant is not detected over a specified time period. The Drinking Water Compliance Monitoring Tablepdf summarizes our monitoring frequencies.

How will I know if a contaminant is found in my water?

Every year, Tucson Water publishes an Annual Water Quality Report for its customers. The results contained in the report are based on compliance data collected from the previous year to comply with the Drinking Water Rules.

The ADEQ also requires that Tucson Water give you public notice should our water supply violate drinking water standards. This includes information about what is being done to correct the situation.

For more information, contact the Customer Support Unit at 520-791-2544.