1. Chlorine

• Source: Used by municipalities as a disinfectant to treat public water supplies.
• Effects: Can lead to a bad taste and smell in water. Prolonged exposure can cause dry skin and other skin irritations.

2. Fluoride

• Source: Added to municipal water supplies to prevent tooth decay; also a natural component in some areas.
• Effects: Overexposure can lead to tooth discoloration and skeletal fluorosis.

3. Mercury

• Source: Erosion of natural deposits, discharge from refineries, runoff from landfills.
• Effects: Can impair brain function and development in both fetuses and children.

4. Arsenic

• Source: Erosion of natural deposits, runoff from agriculture, and industrial production wastes.
• Effects: Can lead to skin damage, circulatory problems, and an increased risk of cancer.

5. Bacteria & Viruses

• Source: Human and animal fecal waste.
• Effects: Can cause gastrointestinal issues, flu-like symptoms, and other serious illnesses.

6. Nitrates/Nitrites

• Source: Runoff from fertilizer use, leaking from septic tanks, sewage, and erosion of natural deposits.
• Effects: Can cause methemoglobinemia or “blue baby syndrome” in infants.

7. Pesticides & Herbicides

• Source: Agricultural runoff, residential stormwater runoff, and commercial use.
• Effects: Long-term exposure can damage the liver, kidneys, lungs, and other organs.

8. Hard Minerals (Calcium & Magnesium)

• Source: Natural deposits.
• Effects: Causes water hardness, leading to scale buildup in pipes and appliances. Can also cause dry skin and hair.

9. PFAS (Per- and Polyfluoroalkyl Substances)

• Source: Used in many industrial and consumer products such as non-stick cookware, water repellent clothing, and some firefighting foams.
• Effects: Associated with adverse health outcomes in humans, including reproductive, developmental, and immunological effects.

10. Cryptosporidium and Giardia

• Source: Human and animal fecal waste.
• Effects: Protozoan parasites that cause gastrointestinal illness, including diarrhea.

11. Radon

• Source: Decay of uranium in soil and rock. It can enter homes through the ground and can also dissolve into underground sources of drinking water.
• Effects: Inhalation can increase the risk of lung cancer. Ingesting water with radon can also pose risks, albeit much lower.

12. Sediments & Particulates

• Source: Erosion, stormwater runoff.
• Effects: While generally not harmful to health, they can affect the clarity and taste of water and can cause wear and tear on plumbing fixtures and appliances.

Remember, the presence and concentration of these contaminants can vary based on the region and the water source. Regular testing of your water supply can help identify which contaminants are present and in what concentrations, allowing for the appropriate filtration and purification measures.