In many areas with limited surface water supplies such as the Western United States or Florida, man has become increasingly dependent on ground water supplies for domestic, industrial, or agricultural use. In Florida, a single aquifer, the Floridan Aquifer, supplies most of the water consumed in the state. Although at first glance ground water supplies may appear enormous, not all the water contained in these aquifers is available for use. In many cases it is too saline (salty) especially in the deeper zones of aquifers. Even where the water is potable, supplies have become increasingly threatened by over-exploitation and pollution. Ground water supplies can be likened to a checking account which starts with a fairly large balance. Ground water can only be conserved (the overall balance remaining constant) if withdrawals from wells and evapotranspiration, and outflow into streams and oceans are balanced by recharge (deposits) from rainfall and inflow. If withdrawals exceed recharge, water levels decline, as is now the case in this state. 

Consider that close to 800 people migrate to Florida each day, and each needs some 150 gallons/day. Each week, water demand in this state increases by some 750,000 gallons/day. It should therefore come as no surprise that water shortages are becoming increasingly common as a result of this increased demand. Population growth also affects recharge areas and the local water budget. As more and more people build houses and roads, the area available for infiltration decreases, more and more water is carried away as runoff in sewers and storm drains and chances for contamination increase. 

The ever-growing use of chemicals (fertilizers, hazardous wastes, petroleum products, insecticides, etc.) by our technological society has led to increased contamination of aquifers. Because many of these chemicals are in solution, it is virtually impossible for them to be removed by the filtering action of the rocks through which ground water passes. Thus aquifers, extremely vulnerable to chemical pollution, are becoming increasingly unfit for human use without prior treatment. 

Ground water has proved to be a boon to those areas plagued by water shortages, and indeed it can be said that it has made deserts bloom. Such obvious blessings have not been without their hidden drawbacks. Remember that all ground water contains some dissolved chemicals. Conventional methods of irrigation are plagued with high evaporative losses (as much as 90% when overhead sprayers are used), leaving the remaining water with a much higher salt content before it even hits the ground. As this water evaporates from the soils to which it has been applied, it leaves these salts to accumulate. In extreme cases, the soil can be rendered unfit for agriculture in a few decades. Nor is this a new problem. Irrigation in the Middle East more than 4,000 years ago destroyed arable land by increasing its salt content to such an extent that these same fields are still unusable even today. 

In Florida, a state that is especially dependent on ground water for its water supplies, intrusion of salt water due to excessive pumping and creation of canals has threatened supplies especially along coastlines.