II.    Water Use and Distribution
    A.    Before 1972, Florida had two water management districts (WMD).
            The South Florida Flood Control District and the Southwest Florida
            Water Management District
    B.    In 1972, three additional WMDs were created based on surface water
            drainage basins: St. Johns River, Suwannee River, and Northwest Florida
            (>Figure 4)
    C.    At present more than 90% of Florida's public water supply is derived from
            groundwater (about 20% of the total use).
    D.    The average Floridian consumes about 800 gallons/day of fresh water (irrigation
            and power generating are two big users); personal use for drinking, washing,
            and sanitation is about 170 gallons/day.  This figure increased about 50 gpd
            in a period of about 10 years (Figure 5).
    E.    Per capita use of salt and fresh water is about 2,200 gallons/day.  The large
            increase is mostly due to power generation that uses a lot of salt water.
    G.    The largest single use is for irrigation (about 40% of the total use) with about
            a 50:50 split between surface and groundwater sources.
    H.    Largest users in Florida are concentrated in most populous counties (Dade,
            Broward, etc.) and large agricultural counties (Polk) (Figure 6).

III.    Hydrologic Setting
    A.    Hydrologic  Cycle
    B.    Water Budget is the balance between inputs (rainfall
           and precipitation) and outputs (infiltration, evapotranspiration, and run-off)
            Retention ponds are a local factor that can increase infiltration.(>Figure 7).
    C.    Rainfall is the only source of fresh water in Florida south of the Suwannee River.
    D.    Rainfall distribution varies with locality from a high of nearly 66 inches in the
            Panhandle to about 64 inches in southeastern Florida to a low of 44 inches in
            the Keys.  There also is an anomalous low rainfall in the area around Tampa
            Bay at about 48 inches.  The statewide average rainfall is about 52 inches; the
            rainfall that occurs in Gainesville (Figure 8).
    E.    Florida Water Budget shows about 150 billion gallons/day (=52 inches of rainfall/year)
            plus 25 bgd from surface inflow (mostly from the Apalachicola River) as inputs (Figure 9).
            Outflow (run-off plus infiltration) is about 68 bgd with evapotranspiration at 107 bgd
            (>Figure 9).  In Gainesville, rainfall is about 52 inches/year (>Figure 8) and evapotranspiration
             is about 46 inches/year (Figure 10) with only 6 inches for run-off and infiltration.
            Florida Keys show a negative balance where evapotranspiration exceeds precipitation on
            average.

IV.    Hydrogeologic Setting
    A.    Peninsular Florida is the emergent part of the Floridan Plateau and is composed of
            thousands of feet of limestones.
    B.    Basic structural setting is controlled by the Peninsular Arch in the subsurface and
            the Ocala Platform at the surface (Figure 11).  This setting (plus the presence of an
            aquiclude)
            is important for creating artesian systems that give rise to the potentiometric surface
            and large springs that occur in North Florida.
    C.    Oldest rocks exposed at the surface are on the west flank of the Ocala Platform
            and are Eocene in age (Avon Park Limestone near Inglis and Crystal River in
            Levy County) (Figure 12).
    D.    The Floridan Aquifer (which furnishes about 60% of Florida's water) covers parts
            of four states (FL, GA, SC, & AL) (Figure 13).
    E.    The potentiometric surface shows highs (i.e., closed contours) in central and north-
            eastern Florida (Figure 14).  These are areas of recharge of the aquifer and are
            very important.
   F.    Some areas of Florida show flowing artesian wells where the surface elevation is
            lower than the potentiometric surface (see the book figure for an illustration).
            Remember that municipal supplies with water towers are man-made analogs
            of flowing artesian systems.
    G.    In many parts of the State, the potentiometric surface of the Floridan aquifer has
            declined as removal of water has exceeded recharge.
    H.    Florida has 27 of the USA's 78 first order springs (100 cubic feet/second of flow
            or 64.6 million gallons/day) (Figure 15).  The three largest springs are (Figure 16):
        1.    Silver Creek Springs
        2.    Crystal River Springs
        3.    Silver Springs (500 million gpd; may be the largest single orifice spring in the world).
        4.    There are some freshwater springs located off the east and west coasts of Florida.
                (Figure 17).
    I.    Other important aquifers in Florida
        a.    Biscayne Aquifer is an unconfined, surficial aquifer located in Dade, Broward
               and Monroe Counties.  It is the second most productive aquifer in the State.
        b.    Intermediate Aquifer in Charlotte and Lee Counties of southwest Florida and
               extending up the east coast to Duval and Nassau Counties.  It is the third most
               important aquifer system and provides water from Port Charlotte to Melbourne.
        c.    Sand and Gravel Aquifers of northwest Florida in Escambia and Santa Rosa
               Counties.  This is the principal source of water for Pensacola and other cities
                in the most western counties in Florida.
    J.    Lakes
        1.    Florida has about 7,800 freshwater lakes of 10 acres or more; about 3,500
                have names
            a.    Lake Okeechobee is the largest (631 square miles)
            b.    Lake George is the second largest (75 square miles)
            c.    Lake Kissimmee is the third largest (54.5 square miles)
    K.    Wetlands-up to 65% of the Florida was once considered wetlands
        1.    Freshwater wetlands-often cypressheads
        2.    Saline and saltwater marshes, often associated with barrier islands

V.    Water Quality
    A.    Highest in upper parts of the Floridan and in the Biscayne
    B.    Intermediate and Surficial Aquifers have low pHs and may be high in
            iron and sulfur.