The natural water quality of groundwater in aquifers is related to the quality of recharge water, the mineralogy of soils and aquifer sediments, the residence time in the ground water flow system, and the presence of nearby saline water. Urban stormwater, agricultural runoff, domestic wastewater, industrial wastewater, and hydrologic modifications are the major sources of water pollution in Florida. Other threats include nitrates from dairy and other livestock operations, fertilizers and pesticides in stormwater runoff, toxic chemicals in leachate from hazardous waste sites, and erosion from construction sites, unpaved roads, and farm fields. Septic tank leachate contributes to the degradation of many water bodies by adding nitrate nitrogen, bacteria, viruses, and synthetic organics used in household cleaning products and septic tank cleaners. Industrial activities can increase concentrations of metals and toxic chemicals, add suspended sediment, increase temperature, and lower dissolved oxygen in the water.
Roadways contribute petroleum pollutants leaked from vehicles and metals from exhaust fumes.
Older sanitary landfills, whose leachate may contain many different chemicals at relatively high concentrations, also pose a threat. The quality of water is determined by making measurements in the field or by taking samples of water, suspended materials, bottom sediment, or biota, and sending them to a laboratory for physical, chemical and microbiological analyses. The concentrations of metals, nutrients, pesticides and other substances are measured in the laboratory. Another way to obtain an indication of the quality of water is biological testing. This test determines, for example, whether the water or the sediment is toxic to life forms or if there has been a fluctuation in the numbers and kinds of plants and animals.