While Big Cypress does not have any active groundwater monitoring network, the USGS and SFWMD have conducted studies of south Florida's groundwater systems. These agencies have worked with Big Cypress staff to install monitoring wells in and around Big Cypress to assess the quality of the groundwater as well as its suitability for use as a drinking water source. The shallow aquifer lies directly below the surface of the Preserve. Because it is so close to the surface, it is constantly affected by surface flows and surface water quality.
The Big Cypress watershed is almost entirely rainfall driven. What this means is that there is no giant river or spring that gives us all of our water. Big Cypress swamp gets an average of 53 inches of rain each year; topography and substrate here keep the rain water from flowing quickly out of the watershed. This slow movement of water from inside the watershed to outside the watershed (to the 10,000 islands and Everglades National Park) is called sheetflow. Because the water moves so slowly across the vast prairies and through the sloughs and strands, water has time to percolate into the limestone substrate, recharging the surficial aquifers.
The aquifers, where water is stored below the surface of the ground, are not huge hollow tanks, filled with millions of gallons of water, but might be imagined as a giant sponge made of limestone, where the limestone does not absorb the water, but does have many holes or fractures where water can percolate and collect. Where the holes or voids are very small, the aquifer may hold water the way a sandy beach would - the water fills the voids between grains of silica or limestone, without seeming to make a space at all. As the water percolates into the groundwater, or flows out to tide, the vegetation, soil and limestone filter and clean the water. Water moving too fast through the system gets less treatment, and water moving too slowly through the system may become stagnant, and lose the benefits of the cleaning it receives from the marsh ecosystem.