Water can become contaminated directly (e.g., a chemical is dumped in a river, in groundwater, etc.), or indirectly (e.g., the water travels through pipes with lead in them).
There are many different types of water contaminants from a wide range of sources, including industrial/agricultural pollution, sewage spills or leaking septic systems, fuel tanks or landfills leaking underground, aging infrastructure, harmful algal blooms in both fresh and salt water. Naturally-occurring contaminants, such as arsenic, copper, iron, lithium, manganese, radon, or uranium present in various geological rock formations, can also contaminate the groundwater in aquifers.
Natural disasters, such as floods, hurricanes, wildfires, earthquakes, or tsunamis pose an immediate threat to sources of drinking water: municipal water systems can be disrupted and private wells can be breached. In such circumstances, safe drinking water may not be accessible to families for days or weeks.
Chemicals or sewage can spread or spill from industrial areas or farms into local drinking water sources. Aging water pipes in need of replacement can contain lead. Water in ponds, lakes, rivers, and oceans, often places where people swim, can also be contaminated with certain chemicals or fecal matter. Algal blooms (an overgrowth of algae and cyanobacteria) can also occur in freshwater or saltwater sources, particularly if the water is warm and/or slow moving,and make people and animals sick.
- Examples of bacteria in water include: Cryptosporidium, E. coli, Giardia, Hepatitis A virus, Legionella, Norovirus, Rotavirus, Salmonella, Shigella.
- Examples of chemicals in water include: arsenic, copper, lead, lithium, manganese, nitrate, perfluoroalkyl substances (PFAS), radon, uranium.
- Improperly discarded antibiotics, hormonal products, and other pharmaceuticals also can contaminate sources of drinking water