The Complex Process Of An Urban Water Supply System

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Have you ever thought about where your water comes from? The question occurred to me when I moved to a southeastern condo community. In my former rural New England home, we had an artesian well. Now we are part of an urban water supply system, and I became curious about the process it takes to provide clean water for our county’s population. So, being the nerd that I am, I accepted an invitation to tour our local water treatment system. I actually found the experience quite fascinating!

It turns out that our southeastern Florida water supply comes from two aquifers.

• One is a shallow 100 foot deep pool of water. It is treated by an 8 million gallon-per-day lime process that’s a combination of pH adjustments with lime, coagulation with a polymer, multi-media filtration, and disinfection with chloramines.
• The deeper Florida aquifer is about 1350 feet deep and is treated by two reverse osmosis facilities. One facility treats 11.15 million gallons per day, and the other treats 22.5 million gallons per day.

Both finished waters are blended, pH adjusted, disinfected, and have added fluoride.

The treatment process in overview: A reverse osmosis process is a multi-step water treatment process. Groundwater is pumped from the two wells onsite where it receives two initial chemicals and passes through a pair of cartridge filters to adjust the pH, remove any larger particles from the water, and prepare it for the next step in the process.

High pressure water is forced through thin, semi-permeable membranes, leaving unwanted contaminants behind. This plant was originally opened in 2006, and its membranes have only recently needed replacing. The clean water, with nearly all of the impurities removed, is blended with some of the groundwater and moves on to the final step in the treatment process. The remaining water left behind, called concentrate, is pumped to one of the wastewater treatment plants nearby.

Following membrane treatment, the water is passed through a degasifier to remove gasses such as hydrogen sulfide (rotten egg smell) that can pass through the membranes and has the pH adjusted. At this point the finished water is ready for disinfection and delivery to the distribution system.

Source water contaminants: Here’s a list of the contaminants that the water facility seeks out for safety and water quality.

1. Microbiological contaminants, such as viruses and bacteria, which many come from sewage plants, septic systems, agricultural livestock operations, and wildlife;
2. Inorganic contaminants, such as salts and metals, which can be naturally occurring or result from urban stormwater runoff, industrial or domestic wastewater discharges, oil and gas production, mining, or farming;
3. Pesticides and herbicides, which may come from a variety of sources such as agriculture, urban stormwater runoff, and residential uses;
4. Organic chemical contaminants, including synthetic and volatile organic chemicals, which are by-products of industrial processes and petroleum production, and also can come from gas stations, urban stormwater runoff, and septic systems; and,
5. Radioactive contaminants, which can be naturally occurring or be the result of oil and gas production and mining activities.

Touring a Water Treatment Facility

The on-the-ground opportunity offered me a visceral look at what it takes to purify 22.5 million gallons of water per day to process water from local aquifers and remove the source water contaminants.

The control center: We enter a control room for the water filtration process. Everything in the water treatment plant is redundant — every function has a backup. A wall of screens hovers above a horseshoe-shaped control center, which monitors all system functions. Interestingly, the facility’s data system isn’t linked to the cloud — that’s for cybersecurity reasons.  Some of the screens display the plant’s exterior, while others feature different graphic images of the filtration system.

Our three control center guides pepper us with information. The gist is that a pumping station pushes water to tanks, through pipes, and then out to customers. If the total distribution lines of this system were to be lined up, end-to-end, they’d add up to 1400 miles of piping.

Ground water needs reverse osmosis (RO) to cleanse it. Bacteria, which is airborne, they say, wants to get fed. Filtration systems strip out chlorine, which invites bacteria. Retention ponds serve to evaporate and filter out contaminants. Flushing water is part of their maintenance program, as it’s needed when low water periods occur.

We look beyond the control center and its screens through windows to an adjacent room, which is filled with enormous columns of tubes. The tubes are stacked eight high and five across. They’re filled with two types of filters that collect contaminants. Each “skid” makes 1400 gallons of purified water per minute and two million gallons of purified water per day — 50 psi enters, and 240 psi exits. The resulting “blended water” is RO with minerals added back in; these minerals are regulated by the EPA.

Test and retest: One stop at the reverse osmosis facility is a relatively small lab, part of the National Environmental Assessment Program that looks at water quality. Think: black cabinets with glass cases. Sinks with hoses jutting off faucets. Chemicals in one gallon containers. Glass front coolers that hold lab samples in progress. Testing kits in plastic buckets. Logs. Temperature gauges. Calculators. Empty sample jars.

Our lab tour guide informs us that “water doesn’t want to be pure — it’s filled with lots of minerals.” We learn that water samples get dechlorinated. Different bacteria are able to be seen under blue light. An autoclave kills off any bacteria under testing. They send  samples out for biological and bacteriological testing using membrane filtration; occasionally, they sample for forever chemicals (ie. PFAS– per- and polyfluoroalkyl substances).

Our tour participants are interested in advice for hard water in their homes. The lab tour guide suggests to flush hot water heaters once per year to keep their coils clean and prolong water heater life. The guide also notes that tankless water heaters don’t need flushing. Another hint we cull is that carbon filters are the best for home use. Plus it’s a good idea to flush your system if you’re away for a period of time. There is a lot of flushing talk going on…

Backup systems in the event of an emergency: We exit outside, and our guide points us to pipes jutting out of the ground. They’re color-coded: blue is for potable water, 80% of which is for consumers. The remaining 20% of water returns to the aquifer. Three generators are on site, and they’re necessary for power intermittency in the event of emergencies like hurricanes.

Final Thoughts about an Urban Water Supply System

Reverse osmosis systems have emerged as key to guard against wastefulness and inefficiency in urban water supply facility operations. Reverse osmosis systems have become a stable method so that facilities and counties can manage their most vital resource of water.

Thomas Boving, professor and chair of the University of Rhode Island Department of Geosciences, is a hydrologist. The tour reminded me of an interview I read with Boving, who is adamant that we have to rethink our relationship with water.

“We have to be cognizant of the limitations of our natural environment and think about the future — that should be on everyone’s minds. We need to change our attitudes toward water. It is a finite resource; high-quality water has a value that must be accounted for properly. And if that means water costs more in the future, well, maybe that incentives us to use less of what we have — and to use it more wisely.”

Resources

• “Water for the world.” Marybeth Reilly-McGreen. University of Rhode Island Magazine. Fall 2024.
• “Water quality report 2024.” City of Port St. Lucie, Utility Systems Department.