DRINKING WATER TREATMENT IN FLORIDA

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How is Your Drinking Water Treated to Ensure Safety?

Source water (sometimes called "raw" water) is pumped through pipelines to a Water Treatment Plant (WTP), where it goes through processes to remove contaminants. 

Many utilities have more than one WTP. There are often multiple wells or other sources. Having multiple facilities provides redundancy, which is especially important in case of emergencies or natural disasters. The WTPs are usually located as close to the source as possible, which reduces the cost for pipeline construction and pumping. 

The type of treatment needed to provide safe drinking water depends upon the quality of the source water. 

For instance, in northeast Florida, most of the water comes from a confined portion of Floridan Aquifer (a confined aquifer) 800 to 1200 feet below the earth's surface. A confined aquifer is one that is covered by a rock, clay, or sediment layer that slows down or prevents groundwater flow. This water is very pure and requires very little treatment, as surface contaminants cannot reach it. The only treatment required is aeration to remove sulfur compounds and disinfection with chlorine.

WTPs in areas where the source water is from an unconfined aquifer or from other sources like rivers, lakes, or seawater, require additional treatment steps. Again, your annual Water Quality Report will explain the treatment steps used in your area.

Here are some typical treatment steps used to ensure the water meets all the regulatory requirements. 

Note that each WTP is unique, engineered and built to provide the specific treatment steps based on the source water quality.

Typical Treatment Steps at Water Treatment Plants (WTPs)

Coagulation and Flocculation
Source water flows into a tank or tanks. Coagulant chemicals, such as aluminum sulfate or iron salts are added to the water to help any suspended particles to clump together. Flocculation uses gentle stirring to help the clumped particles become larger and heavier.

Sedimentation
The water then flows into a sedimentation basin. With no stirring, the heavy particles sink to the bottom of the basin, leaving clear water above. The clear water at the top flows to the next treatment step, while the solids at the bottom (called sludge) flows to another tank for additional treatment and disposal.

Filtration
Several type of filtration can be used to further treat the water. WTPs may use one or more of these filtration steps, depending again on the source water quality:
  • Sand Filtration - water is filtered through layers of fine sand (and sometimes gravel) to trap particulates and contaminants. An interesting discussion of sand filtration is found here.
  • Granular Activated Carbon (GAC) - GAC is often used to remove organic contaminants and to improve taste and odor. It may be used prior to membrane filtration to prevent organic fouling of the membranes.
  • Membrane Filtration - Pressure is used to force water through a semi-permeable membrane. This process can remove very small particles, microorganisms, dissolved salts, and other contaminants. There are four main types of membranes, based on the size of the pores that the water passes through:
    • Microfiltration: Pore size is between 0.1 to 5.0 microns, small enough to remove bacteria.
    • Ultrafiltration: Pore size is between 0.01 to 0.1 microns. These filters can remove even smaller contaminants, such as viruses.
    • Nanofiltration: Pore size ranges from 0.001 to 0.01 microns, and can remove most organic salts. This type of filtration is sometimes used for water softening.
    • Reverse Osmosis: Pore sizes are les than 0.001microns. Reverse osmosis is typically used to treat brackish or seawater.
Disinfection
Disinfectants are added to the water to destroy any remaining pathogens (disease causing microorganisms). Disinfectants are introduced for either primary disinfection or secondary disinfection. 
  • Primary disinfection may be completed within the WTP as part of the treatment process. Chemicals that might be used for primary disinfection include:
    • Chlorine
    • Chlorine dioxide
    • Ozone
    • Ultraviolet light
  • Secondary disinfection is performed just before the water enters the pipelines that send the water to your tap. In Florida, secondary disinfection must use a chemical that can be measured at various points in the pipelines. Therefore, the chemicals used are either:
    •  Chlorine or 
    • Chloramine (a combination of chlorine and ammonia)
    • A chlorine residual of at least 2 parts per million must be present throughout the system and at the furthest point from the WTP.

Here's a video from the Coral Springs Improvement District describing their process. Coral Springs' water source is the Biscayne Aquifer:



And here's a video about Tampa Bay Regional Surface Water Plant. The water source for this WTP is local rivers:


This treatment plant is currently undergoing a $181 million expansion.

And here is a video about Tampa Bay's Seawater Desalination Plant:



A Word About Chlorine. . .

I've heard people complain about having chlorine in their tap water. They don't like the way it smells or tastes - or they worry that it is harmful to their health.

Chlorine should be celebrated, as this chemical has saved billions of lives. Before its use, many people died from waterborne diseases like cholera. 

If you are worried about drinking chlorine, you can fill a jar with water - but leave some space at the top and let it sit. The chlorine will dissipate. Or even better, use something like a Britta water pitcher. The activated carbon filters in these pitchers remove chlorine. 

Want to Learn More?

The Center for Disease Control (CDC) has a very good simple summary of water treatment steps.

There's also a good discussion of the treatment steps from Science and Technology Research News.

Waterlyst provides a nice discussion and explanation of the various filtration methods.

Here's a short YouTube video from Denver Water explaining the water treatment process.

 Geek Out

Florida Department of Environmental Protection (FDEP) Source & Drinking Water Program

You can check out FDEP's Drinking Water Rules

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