When rain falls and seeps deep into the earth filling the cracks crevices and porous spaces of an aquifer basically an underground storehouse of water it becomes groundwater one of our least visible but most important natural resources. Nearly 40 percent of Americans rely on groundwater pumped to the earth’s surface for drinking water. For some folks in rural areas it their only freshwater source. Groundwater gets polluted when contaminants from pesticides and fertilizers to waste leached from landfills and septic systems make their way into an aquifer rendering it unsafe for human use. Ridding groundwater of contaminants can be difficult to impossible as well as costly. Once polluted, an aquifer may be unusable for decades, or even thousands of years. Groundwater can also spread contamination far from the original polluting source as it seeps into streams lakes and oceans. When contamination originates from a single source it called point source pollution. Examples include wastewater also called effluent discharged legally or illegally by a manufacturer oil refinery or wastewater treatment facility, as well as contamination from leaking septic systems, chemical and oil spills and illegal dumping. The EPA regulates point source pollution by establishing limits on what can be discharged by a facility directly into a body of water. While point source pollution originates from a specific place, it can affect miles of waterways and ocean. It goes without saying that water pollution can be contained by a line on a map. Transboundary pollution is the result of contaminated water from one country spilling into the waters of another. Contamination can result from a disaster like an oil spill or the slow, downriver creep of industrial agricultural or municipal discharge.