Water Quality Summary of Main Distribution System

The information in this table is based on water quality monitoring results for the most recent 12-month period.

Water Quality Measure	Water Quality Measure Results
	Average	Lower Limit	Upper Limit	Number of Samples
Chlorine, mg/L	0.87	0.57	1.14	2861
Coliform Bacteria, % Pos.	0.07	N/A	N/A	2877
Fluoride, mg/L F	0.41	0.21	0.63	982
Hardness, mg/L CaCO3	200	92.32	263.92	948
Nitrate as Nitrogen, mg/L N	1.44	0.59	2.76	982
Sodium, mg/L Na	56.0	32.0	70.0	949
Temperature, Deg.F	79.5	64.2	91.7	2821
Total Dissolved Solids, mg/L	417.0	190.1	540.7	2760
Total Trihalomethanes, ug/L	9.8	0.0	17.472	35
pH, Std. Units	7.89	7.58	8.13	2819

• As part of the Quality Assurance process this data is checked after posting on the web site. We are providing upper and lower limits to ensure that sampling errors do not appear here. The average is derived from all samples, while the upper limit is the 95th percentile and the lower limit is the 5th percentile (two standard deviations).
• Lower and upper limits do not apply to Coliform (N/A = Not Applicable).
• Chlorine residual measures the free available chlorine in drinking water. Chlorine is used to maintain continuous disinfection throughout the distribution system. The EPA's maximum limit for chlorine residual is 4.0 mg/L on average. In order to ensure your drinking water is protected, Tucson Water's chlorination goal is to maintain a detectable level of chlorine at all times throughout the system.
• Coliform bacteria indicate the overall bacterial quality of drinking water. Monitoring for coliform bacteria throughout the distribution system is required. State and Federal standards limit the number of total coliform positive samples to 5 percent of the total number of samples collected each month in Tucson Water's main distribution system for Water Quality Zones 1-10. The Distributed Water Quality Summary report displays the percentage of samples that were positive over the most recent twelve months and represents only the main distribution system.
• Fluoride is a naturally occurring constituent in drinking water. The drinking water standard for fluoride is 4 mg/L on average. The optimum fluoride level for drinking water is 0.8 mg/L. Where the fluoride level of drinking water is less than 0.6 mg/L, supplements may be worthwhile depending on the individual situation. Please see your medical provider.
• Hardness is the measure of calcium and magnesium in drinking water. Hardness levels in Tucson's water vary from around 40 to more than 300 mg/L CaCO3. (If you have a water softener, you can calculate the grains per gallon of hardness by taking the mg/L value and dividing by 17.1)
• Nitrate as Nitrogen can occur in drinking water supplies from both natural sources and human activities (such as fertilizer use, munitions manufacturing, and septic systems). The EPA's health-based limit for nitrate as nitrogen in drinking water is 10 mg/L - all of Tucson's water supplies have nitrate as nitrogen levels below this limit.
• Sodium is a naturally occurring constituent in drinking water, and typically originates as water dissolves rocks and soils as it flows in streams and rivers or percolates underground. A sodium content of 20 mg/L or less in drinking water meets EPA's guideline for 'sodium-free' diets.
• Total dissolved solids (TDS) is a measure of the mineral content of drinking water. There are no health-based limits for TDS in water.
• Total Trihalomethanes (TTHM) is the composite sum of chloroform, bromoform, chlorodibromomethane, and bromodichloromethane. These compounds are formed when chlorine is added to water that contains dissolved organic material. The drinking water limit for TTHM is currently 80 ug/L (micrograms per liter). The City of Tucson has set a local limit of 20 ug/L. Tucson's TTHM levels are very low.
• Temperature is the water temperature in Tucson's distribution system. This typically ranges from 60^o to 90^o F over the course of the year.
• The pH of a water measures the water's balance of acids and bases. A pH of 7 is considered neutral with lower pH values representing an acidic water and higher pH values representing a more basic or alkaline water. Tucson's water supply is slightly alkaline, averaging between 7.5 and 8.2 in the distribution system.
• For more information on water quality, see our Terms and Definitions page.