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      How Safe is Your Drinking Water?  >  Groundwater and Surface Water

Groundwater and Surface Water

In order to understand drinking water contamination, it is necessary to first understand from where our drinking water comes. For most urban residents, relying upon municipal water systems, drinking water comes from two major sources: groundwater and surface water. These two sources of drinking water will be referenced throughout this guide to water contamination.

Groundwater refers to any subsurface water that occurs beneath the water table in soil and other geologic forms (Rail, 2000). Scientists estimate that groundwater makes up 95% of all freshwater available for drinking. Groundwater is a significant source of water for many municipal water systems in the United States. Rural residents, withdrawing their water from wells, also rely upon groundwater.

Surface water refers to water occurring in lakes, rivers, streams, or other fresh water sources used for drinking water supplies. While most drinking water in the United States is withdrawn from groundwater sources, surface water remains a significant water resource.

Each source of water has a unique set of contaminants; groundwater stores pesticide chemicals and nitrate while surface water contains most bacteria and other microorganisms. Because of the interconnectedness of groundwater and surface water, these contaminants may be shared between the two sources. Neither water source can ever be entirely free from water contaminants. Due to the cycle of water (hydrology), the two sources of drinking water feed each other, sharing contaminants.

Groundwater is generally stored in aqueducts, underground layers of porous rocks that are saturated with water. These aqueducts receive water as soil becomes saturated with precipitation or through stream and river runoff. As the aqueducts exceed their capacity for water storage, they will bleed water back into streams or rivers. The aqueducts maintain a natural balance of water, alternately receiving or giving water as their saturation levels oscillate. Throughout this process, water constantly moves between surface and groundwater sources, sharing contaminants.

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How Safe is Your Drinking Water?
Introduction - The Value of Drinking Water
Groundwater and Surface Water
Herbicides and Insecticides - History & Occurrence
Herbicides and Insecticides - Specific Chemicals and Health Effects
Nitrate
Volatile Organic Chemicals (VOCs)
Chlorine
Chlorine Byproducts
Fluoride - Recent Discoveries
Fluoride - Adverse Health Effects
Lead
Mercury and Arsenic
Bacteria and Viruses
Protozoa
Human and Animal Feces
Conclusion - The Importance of Drinking Filtered Water
References
 
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