The Safe Drinking Water Act (or SDWA) is a U.S. law that was passed in 1974. Drinking water that is free from contaminants is essential to human health. Two thirds of the human body is water and water influences every process in the body. The SDWA and regulations passed by the Environmental Protection Agency (or EPA) set maximum levels for various contaminants in drinking water. They also specify treatment techniques for removing these contaminants. The SDWA defines four classes of contaminants:

  • Physical
  • Chemical
  • Biological
  • Radiological

Water containing these contaminants may be referred to colloquially as \”dirty water\” or \”polluted water\” and water that is free from these contaminants as \”clean water.\” However, the SDWA does not define any of these phrases. Thus, \”dirty water\” could contain contaminants from any of the four categories. Here are brief descriptions of the classes from the SDWA:


Physical contaminants are what most people would associate with dirty water. According to theĀ EPA, physical contaminants affect the appearance of water. Physical contaminants include inorganic debris, such as dirt, sand, and clay, as well as suspended organic matter, such as leaves, seeds, and pollen. Strictly speaking, insects also fall within the category of physical contaminants, since biological contaminants (discussed below) is limited to microorganisms.

Physical contaminants are removed from drinking water through filtering systems and settling tanks. Generally speaking, physical contaminants are the easiest contaminants to treat.


Chemical contaminants are more often thought of as causing \”polluted water\” rather than \”dirty water.\” However, chemical contaminants can come from natural or man-made sources. Thus, copper that is naturally occurring and copper that results from mining runoff or industrial waste is considered to be the same chemical contaminant.

This category includes many organic and inorganic chemicals, including some well known contaminants, such as arsenic, lead, dioxins, nitrites, and nitrates.


    • Arsenic is a naturally occurring chemical element. Arsenic can also result from industrial waste. Arsenic is toxic and has been linked to cancer, liver problems, and neurological problems after long term exposure.
  • While lead can occur naturally in some communities, it is of greatest concern in cities with aging water delivery systems that use lead pipes. Lead is a neurotoxin that can lead to brain damage and behavioral problems.
  • Dioxins are among the most dangerous pollutants regulated by the EPA due to their severe health effects and their persistence in the environment. Dioxins damage the reproductive system and immune system.
  • Nitrites and nitrates can occur naturally in the soil. However, many of the cases of contamination occur due to runoff from fertilized agricultural fields. Exposure to nitrites and nitrates is particularly dangerous to infants who lack the ability to process nitrites and nitrates and can die from a condition called blue baby syndrome.


Chemical contamination can also be caused by pharmaceuticals that are improperly disposed of. For example, prescription drugs that have been flushed down the toilet can contaminate water even after the water is treated and returned to the environment.


Many people who have traveled extensively have experience with the inconsistent drinking water in developing countries. More often than not, traveler\’s diarrhea is caused by microorganisms, such as parasites, bacteria, protozoa, and viruses, contaminating drinking water and food washed with contaminated water.

Examples of microorganisms that the EPA regulates in drinking water include cryptosporidium, giardia lamblia, legionella, E. coli, and enteric viruses. These microorganisms can cause diarrhea, vomiting, and stomach pain when ingested. While most people will recover after a few days, people with weak immune systems, young children, and the elderly are particularly at risk of complications or death.


Radiological contaminants are exactly what they sound like – radioactive elements such as uranium and radium. Medical waste can be a source of radiological contamination since many diagnostic tools (such as x-ray machines) and treatments (such as cancer treatments) use radioactive materials.

Long term exposure to radiological contaminants can increase the risk of cancer. Also, radiological contaminants can lead to kidney problems since the kidney\’s function is to filter waste in the production of urine.

\”Dirty water\” is not in the eye of the beholder. While physical contaminants can be seen, other contaminants, such as chemical, biological, and radiological contaminants are usually not visible to the naked eye. Although they are invisible, these contaminants can have serious health consequences, particularly after long term exposure.