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Treatment & Supply

St. Petersburg Water Treatment and Distribution System
As the largest city in Pinellas County, St. Petersburg is home to approximately 250,000 residents. The Water Resources Department provides potable drinking water to these residents, yet draws none of its fresh water supply from the ground directly below the city. 

St. Petersburg's Drinking Water Supply
In the late 1800's, as people came to settle in this area, spring-fed Mirror Lake was the primary source of drinking water. However, by the 1920's Mirror Lake was showing evidence of salt water intrusion. Coupled with concerns due to increased demand, the early city leaders went in search of a high quality water source to supply the growing city. It was found in Northwest Hillsborough County, and in 1930 a 26 mile pipeline was constructed to carry fresh water from deep wells located there to the city. 

As St. Petersburg and the Tampa Bay area have continued to grow and change, so has its source of water. Today we not only receive water from groundwater supplies, like those described above, but we are also receiving surface water from rivers, and desalinated water. These source waters are blended together and transported to the Cosme Water Treatment Plant where it undergoes a three-step treatment process, which includes aeration, softening and filtration takes place. Fluoride is added to the water to provide protection against dental decay.

  • Aeration helps to remove tastes and odors, primarily hydrogen sulfide when Cosme is receiving only well water. With the use of blended waters, the source water will vary. At times, aeration is used to bring the water to the head of the plant.
  • Lime Softening helps to adjust the naturally occurring water hardness (caused by dissolved calcium and magnesium), when Cosme is receiving proportionately large amounts of groundwater. Lime softening helps to reduce the amount of soap needed for laundry and bath, lessens staining on bath and kitchen fixtures, and can help prevent clothing wear and tear. In addition, lime is used for alkalinity adjustment.
  • Filtration removes bacteria and other microorganisms and provides aesthetically pleasing, sparkling clean water for drinking. Disinfection of drinking water is required to inactivate bacteria, viruses or other microorganisms which might be present.

Tips for maintaining your private plumbing

Disinfection With Chloramines
All of the city's potable water is disinfected using chloramines (a combination of chlorine and ammonia) which is a proven, safe method used throughout the country. 

Chloramines must be removed from water before it can be used for kidney dialysis or for fish and aquatic life because chloramines are harmful if they directly enter the bloodstream. 

All kidney dialysis patients, even those who receive treatment from a caregiver must be under the care of a kidney dialysis center. All centers in Pinellas, Pasco, and Hillsborough counties, as well as hospitals with acute dialysis facilities, are aware of the proper procedures to remove chloramines. 

Since fish and aquatic animals obtain oxygen directly through their gills, directing water into their bloodstream, it is important to remove chloramines from the water before keeping live saltwater and fresh water fish and other aquatic life including Koi fish, lobster, shrimp, frogs, turtles, snails, clams, and live coral. Local pet suppliers have de-chloramination products. Chloramines do not dissipate when water is left to sit, as it does with chlorine. 

Water Filters
If you use a water filter, it is very important that you follow the manufacturer's recommendations for filter replacement in order to assure effective and safe filtration. Consider the cost of proper maintenance before purchasing a water filter. 

Many filters are designed to neutralize chlorine but will not remove the ammonia from chloraminated water. Ammonia can become a food source for bacteria that may proliferate in filters that are not replaced regularly.

Toilet Flappers
Chloramines may wear out the rubber inner workings of the toilet, especially mechanisms like the toilet flapper. It is advisable to inspect your toilet flapper once or twice a year to ensure that it is functioning properly. 

Replacement parts are inexpensive compared to the cost of water lost through toilet leaks. Flappers which are inexpensive often contain more plastic which is less likely to deteriorate in chloraminated water.

Award Winning Water Treatment Plant
The Cosme Water Treatment Plant is dedicated to being the best operated water treatment plant in the state of Florida. This is demonstrated by the impressive collection of awards won on numerous occasions:

  • The Florida Department of Environmental Protection's (Southwest District) Excellence Award for Outstanding Operation
  • The American Water Works Association's Outstanding Water Treatment Plant Award
  • The Environmental Protection Agency's National Division (Southeast States) Excellence Award representing the State of Florida

From Us to You

The quality drinking water you receive travels from the Cosme Water Treatment Plant to two distribution pumping stations. At times, the disinfection level may require additional adjustment before distribution to St. Petersburg water customers.

The Water Resources Department maintains a 24 hour/day, 7 days/week emergency dispatch center at 727-893-7261.

If you have a water quality concern you may call the Water Quality Info Line at 727-893-7261. Please leave your name, address, and phone number along with a brief description of the problem. A Water Resources representative will contact you.

If you have questions about our source water or chloramination, contact our wholesale water supplier, Tampa Bay Water at 727-796-2355 or on the web at

If you have questions about the Cosme Treatment Plant, call 727-551-3708.


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