What Lies Beneath

Florida’s aquifers are both vital and vulnerable.

Living in Florida we’re probably more aware of water than residents in many other states. It’s a peninsula, after all, so we’re surrounded by the Atlantic Ocean and the Gulf of Mexico, not to mention all the rivers, lakes and springs we’re fortunate to have nearby. 

Despite all that visible water, our primary source of water is groundwater, which comes from underground aquifers. 

According to the Florida Department of Environmental Protection, most of Florida’s public water systems use groundwater, drawing from approximately 12,000 wells that connect with five major aquifer systems.

Notice the “s” on the end of that word. Yes, there’s more than one aquifer beneath our sandy soil. The largest of these is the Floridan aquifer system, which underlies not only all of Florida but parts of Georgia, Alabama and South Carolina, extending for about 100,000 square miles. 

Four additional aquifers supply water in Florida: the sand and gravel aquifer (western Panhandle area), the Biscayne Aquifer (South Florida), the intermediate aquifer system (southwestern Florida), and the surficial aquifer system (any otherwise undefined aquifers that are present at the surface).

So long as the average person can turn on the tap and water comes out, it’s safe to say they probably don’t think much about where that water comes from. But as residents of a popular state with an ever-increasing population, we’d be wise to learn more about the remarkable, yet vulnerable, aquifer systems we depend on.

In A Nutshell

If you could take a giant vertical slice out of our part of the state and look at it from the side, you’d see a relatively thin layer of surface material (soil, sand, clay) at the top. Underlying that, you’d see a vast area of porous carbonate rocks. 

Because that rock material (mostly limestone and dolomite) is permeable, it not only holds water but allows water to move through its holes, cracks and fractures. Filling those openings are both fresh and saltwater. Freshwater is found in the upper part of the aquifers, while saltwater, which is heavier than fresh, is found at greater depths.

The Floridan aquifer averages 1,000 feet thick. In the central part of the state, the freshwater layer is thickest and can extend as deep as 2,000 feet below the surface. Toward the coast and the southern part of the state, that freshwater layer gets much thinner.

Growing Population

“The Floridan aquifer system is one of the most prolific water-bearing aquifers in the world. The nature of the limestone, caverns and fractures in the limestone allow large volumes of water to move freely,” explains Scott Laidlaw, a professional geologist and bureau chief for water supply planning and assessment for the St. Johns River Water Management District.

One of five regional water management districts established by the state Legislature in 1972, the St. Johns River Water Management District covers 18 counties (12,283 square miles) in northeast and Central Florida, including Marion. As environmental regulatory agencies of the state of Florida, these management districts are tasked with “ensuring a long-term supply of drinking water, and to protect and restore the health of water bodies.” (The districts work with public water utilities but don’t supply water themselves.)

As might be expected, the increasing number of Florida residents is a very real concern for these agencies. 

“One of the biggest challenges we face is a growing population and greater demands on our resources,” notes Laidlaw. “When we determine regions where groundwater alone can’t meet all the projected demands, we’re required to create water supply plans. All five of the districts in the state conduct regular water resource assessments to evaluate the potential effects of supplying the demands for water with only groundwater.”

The 18 counties in the St. Johns district alone are anticipating a population of 6.7 million people by 2020 with an expected water use of 1.3 billion gallons per day.

Our district alone is currently using just over 1 billion gallons per day. Keep in mind this doesn’t include such densely populated areas as South Florida or the southwestern portion of the state.

Utilizing Technology

“The district has always looked at innovative ways to get water back into the aquifer,” says Laidlaw, noting that an ongoing effort is finding ways to reclaim water and reuse it, rather than pulling more water from the aquifers.

Reclaimed water is wastewater that has been treated and disinfected. Although this water is termed “non-potable” (not intended for drinking), it can be distributed for irrigation purposes, cooling power plants, etc.

 “In Ocala, we have the Pine Oaks Wetlands Recharge Project to bring reclaimed water and storm water back into the aquifer system,” says Laidlaw. “These types of projects can be very beneficial to the system and bring in water that might otherwise just run off.”

The St. Johns district set a record for highest reclaimed water used beneficially in 2017 at 223 million gallons per day. District wide, more than 50 percent of wastewater flows have been reused beneficially since 2010. Alachua County leads the pack with an impressive 96 percent countywide reuse utilization rate. 

Laidlaw adds that existing technology is also being used to bring treated reclaimed water up to standards so that it can be used for human consumption.

“This technology is being used across the country and in other countries,” he says. “If we can use reclaimed water, we don’t have to pull so much water out of the ground, and if we don’t take it out of the aquifer system, the whole system benefits.”

Saltwater Intrusion 

Because the entire state is underlain by brackish water and saltwater, there is always a risk of that salty water mingling with fresh. Not surprisingly, this tends to be a manmade issue.

“As groundwater is pumped out, this reduces the pressure in the aquifer, which can allow vertical migration of brackish/saltwater upward, which is known as ‘saltwater intrusion,’” Laidlaw explains. 

Saltwater intrusion can also occur when wells are drilled too deep.

He points out that there is a greater potential for saltwater intrusion along the coast where seawater can migrate horizontally, in addition to the upward movement of saltwater from the depths of the aquifers.

“Pumping too much groundwater along the coast can cause saltwater intrusion, which can create a negative impact on our springs and rivers,” says Laidlaw. “The whole planning process has to allow the environment to have the water it needs, as well as for the growing population. It’s a balancing act.”

Drop By Drop  

Pay a visit to the incredibly scenic springs and rivers in our part of Florida and it’s hard to imagine worrying about having enough water. But the fact is, the only way the aquifer systems “recharge” is through rainwater.

Florida averages 51 inches of rain per year. Last year we received 58 inches, making 2017 the wettest in a decade. As of July 2018, counties in the St. Johns district had already received 51.01 inches, meaning this year is set to surpass 2017’s impressive stats. 

With all this rain, those aquifers should be full to overflowing, right? Unfortunately, a great percentage (75 percent or about 38 of those 51 inches) of rainfall never reaches the aquifers. About three-fourths of the annual average rainfall evaporates or runs off into lakes, rivers and streams.

“The recharge of aquifers from rainwater can be as little as one inch per year to more than 12 inches,” notes Laidlaw. “In areas where (soil) sediments are thicker, the recharge is less.”

Keeping It Clean

Areas where recharge is higher are also at greater risk of carrying contaminated water into the aquifer. For example, sinkholes offer a greater opportunity for material in the water to enter the aquifer system, so this increases the risk of contamination.

“Springs are like a window on the aquifer. They reflect the health of the system because they are a direct conduit to the aquifer,” says Laidlaw.

It doesn’t take a large amount of a hazardous substance to cause contamination. For example, if someone dumps used motor oil on the ground (which is illegal, by the way!), the oil can mingle with water as it percolates down through the soil and eventually make its way into the aquifer.

“Essentially, whatever you dump on the ground has the potential to seep into the water table and migrate whichever way groundwater is moving, so that contamination can reach the aquifer,” Laidlaw notes. “Everyone needs to be responsible for what they put on the ground.” 

This includes used oil, pesticides and fertilizer, as well as underground fuel storage tanks, which can leak and migrate into the drinking water supply.

“If people don’t act responsibly, these elements can find their way into the groundwater, and once they’re in the aquifer system, it’s very difficult and expensive to get them out of the system,” says Laidlaw.

You may have heard that water from a deep well is better than from a shallow one. Generally speaking, this applies to the aquifer system, as well, simply because the deeper the aquifer, the less susceptible it is to contamination. 

Doing Your Part

“Conservation is critical and is the least expensive way to save water,” observes Laidlaw. “It really boils down to using water wisely.”

Upgrading two commonly used appliances—washing machines and toilets—can significantly reduce water usage for the average household.

According to Consumer Reports, older agitator top-loading washing machines used more than 40 gallons of water for an average-sized load. Manufacturers must meet tougher federal standards now, meaning modern washers use far less water. Newer models require just 13 gallons or less to do an eight-pound load.

Toilets are responsible for nearly one-third of household water usage. The more people in a household, the more water can be saved simply by replacing old toilets with newer low-flush models. Low-flush toilets use about 1.28 to 1.6 gallons per flush, as compared with old models that use a whopping five to seven gallons each flush.

“Turning off the faucet while brushing your teeth sounds simple, but it saves about one-half gallon of water per day,” says Laidlaw. “If you have 20 million people doing this, that’s 10 million gallons of water. Collectively, it adds up!”

Water Restrictions

Nearly half of all residential water use goes to lawn and landscape irrigation. Restrictions are in place year-round when it comes to irrigation. This applies to everyone, whether you’re in the city and use public water or live in the country and have your own well. 

Time of year Addresses ending in odd number or no addresses Addresses ending in even number Non-residential properties
Daylight saving time Wednesday/Saturday Thursday/Sunday Tuesday/Friday
Eastern Standard Time Saturday Sunday Tuesday
  • Water only when needed and not between 10am and 4pm.
  • Water for no more than one hour per zone.

For additional information about the watering restrictions, please call (800) 232‑0904.

How You Can Help

With a few simple tweaks to your routine, you can save water and help protect aquifer systems.

  • Turn off water when brushing your teeth and washing your face.
  • Only run the dishwasher or washing machine with a full load.
  • Fix leaking/dripping faucets and toilets. Those drips can add up to thousands of gallons a month!
  • Install low-flush toilets, showerheads and newer-model washing machine.
  • Water lawns wisely and only when needed.
  • Collect rainwater for garden and outdoor use. 
  • If you have an irrigation system, utilize a rain sensor to avoid unnecessary water use. 
  • Follow watering restrictions for your area.
  • Maintain a landscape with Florida native plants, which require minimal care and water.
  • Take care when using fertilizers, pesticides, etc. Follow label directions carefully to avoid runoff, and don’t over use.
  • Dispose of used oil and petroleum products only at designated disposal areas; never dump them on the ground.
Learn more › To find out just how much water you’re using and ways to save, visit the St. Johns River Water Management District website at sjrwmd.com. Under the Menu tab, click on Water Conservation, and then click on Home Water Use Survey. 
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