Common Water Contaminants Guide

It wasn’t too long ago that sanitary conditions in the United States and around the world were much more toxic.

In fact, even in a lot of developing countries water contamination is still a horrible problem that societies face.

Contaminated water can cause all kinds of diseases, food poisoning, and as a result a poorer quality of life due to the effects it produces on the health and economic activity of a population.

In this article, we will outline the most common water contaminants as well as how water actually becomes contaminated so that you can make sure you are getting clean water that’s good for your body while also determining if you need a water filter.


Main Categories of Water Contaminants

Water is safe to drink only when it is free of disease-causing organisms and toxic chemicals.

Below are the main 7 types of water contaminants that can potentially cause health problems at large enough amounts.

  1. Microbiological
    • Algae
    • Bacteria
    • Diatoms
    • Fungi & Mold
    • Worms & Protozoa 
    • Viruses
  2. Organic chemicals (contain carbon)
    •  MTBE-methyl tertiary-butyl ether 
    •  PCBs- polychlorinated biphenyls 
  3. Byproducts of Drinking Water Disinfection
    • THMs- trihalomethanes
    • HAA5s- haloacetic acids
  4. Inorganic Chemicals
    • Arsenic
    • Chromium VI
    • Chloride
    • Hydrogen Sulfide
    • Lead
    • Heavy Metals
    • Nitrates
  5. Corrosion Products
    • Iron
    • Lead
    • Copper
  6. Radiological (natural radiation or man-made like X-rays)
    • Radium
    • Uranium
    • Gross Alpha Particles
  7. Unregulated emerging contaminants
    • Pharmaceuticals
    • Personal care products
    • Endocrine disruptors

It’s important to note that the presence of a contaminant in the water supply does not necessarily pose a health risk. This is because most drinking water may contain some amount of a type of contaminant. 

It depends more on the type and amount of the contaminant. Some contaminants may be safe at small levels while others may not be.

This is why the US EPA has drinking water regulations where they set legal limits on over 90 contaminants in drinking water. The legal limit reflects the level of contaminant that protects human health and which our water facilities can achieve with the best available technology.

Now, let’s dive into the specific contaminant categories a little more below.

Microbiological Contaminants

Microbes are found everywhere including in and on our bodies. All living species need microbes to survive and they play a vital role in the health of the planet.

That being said, there are also disease-causing microbes (also known as pathogens) that can be toxic when found in drinking water or on contaminated food.

Microorganisms are the most common cause of waterborne illness in the U.S. today.

Below are the most common pathogens you should be aware of.

Blue-Green Algae

  • Found in surface water 
  • Can produce toxins which survive water treatment
  • Microcystis, Anabaena, and Aphanitomenon can cause diarrhea


  • Most of the bacteria in our bodies are harmless and actually beneficial 
  • However, some species are pathogenic and can cause disease if ingested
  • If a pathogen is consumed in water, it will infect the GI tract
  • The following are conditions that can occur:
SalmonellaTyphoid, Diarrhea
Vibrio choleraDiarrhea
Yersina enterocoliticaDiarrhea
Legionella pneumophiliaAcute Respiratory
Microcystis, Anabaena, AphanitomenonDiarrhea, possible carcinogens

This technical information was sourced from the Water Quality Association Learning Resouces.

Organic Chemicals & Byproducts of Disinfection

Organic chemicals and byproducts of disinfection can cause numerous different health risks including cancer and it’s best to keep them in check.

Organic Chemicals

  • Water supplies can contain dissolved organic chemicals which come from man-made activities including insecticidespesticidesherbicides, and the gasoline additive MTBE also known as methyl tertiary-butyl ether
  • These chemicals usually have more chronic health effects since they are usually in smaller amounts in the water supply
  • Other organic chemicals that can leak into water from chemical spills are trichlorethylenetetrachlorethylenepolychlorinated biphenyls (PCBs), and dioxin
  • A lot of organic chemical contaminants can be cancer-producing which is why it’s important to limit these chemicals in your water

Byproducts of Disinfection

Disinfection byproducts are created from the reaction of chlorine used to disinfect water with humic and fulvic acids present from vegetation decay. 

These are important to consider because most city water runs through a local water treatment facility where they use disinfectant chemicals to make sure the water meets general standards.

Trihalomethanes (THMs)

  • Byproduct of disinfectant process to control microbial contaminants
  • Group of four chemicals: chloroform, bromodichloromethane, dibromochloromethane, bromoform
  • This chemical has been shown to have negative effects on the liver, kidney, central nervous system, as well as increase the risk of cancer

Haloaecetic Acids (HAA5s)

  • The regulated haloaecetic acids are: monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid, and dibromoacetic acid
  • Ingesting these chemicals suggest they may increase the risk of cancer

Inorganic Chemicals & Byproducts of Corrosion

Inorganic chemicals are rarer and usually founder in smaller quantities of drinking water but they can be very toxic. Byproducts of corrosion can come from pipes or other fixtures that transport water to your home.


  • Enters groundwater through erosion or from man made sources like petroleum production or semiconductor manufacturing
  • Higher levels of arsenic are usually found in groundwater sources compared to surface water sources
  • Arsenic is toxic to humans at as little as 100 mg which can cause severe poisoning
  • Can only detect arsenic with water testing since it’s colorless and tasteless
  • The western US usually has higher levels of arsenic in the water systems

Chromium VI

  • There are 3 types: metallic chromium, trivalent chromium, and hexavalent chromium
  • Metallic chromium doesn’t occur naturally but it is used to make steel and alloys
  • Trivalent chromium occurs naturally and can be found in rocks, soil, and foods. Not considered a major health risk
  • Hexavalent chromium does not occur naturally. It is the most toxic and considered a health risk which can cause intestinal issues, allergies, liver damage, and more.

Hydrogen Sulfide

  • Colorless gas that has a rotten egg odor
  • In residential areas hydrogen sulfide most commonly results from decomposition in septic or sewer systems
  • Hydrogen sulfide can cause chronic health effects in humans and because of its toxicity, adversely affect aquatic organisms
  • It can affect the central nervous system causing symptoms like dizziness, nausea, headache, and more.

Lead (Byproduct of Corrosion)

  • Metallic element that is toxic to humans
  • Lead does not typically come from source water but water from the point of use due to corrosion of pipes
  • Lead can enter home drinking water by leaching from service connections, copper piping, or brass fixtures
  • The human body can be severely damaged by lead. Lead poisoning doesn’t show any symptoms but signs such as irritability, weight loss, vomiting, constipation, and stomach pain can occur from it as well as other health problems.


  • Found naturally when nitrogen combines with oxygen
  • No visible color, taste, or odor
  • Can also be released in smoke and industrial or auto exhaust
  • Presence of nitrates in water indicates possible pollution of the water with animal waste

Copper (Byproduct of Corrosion)

  • Copper is used in household plumbing materials
  • It enters the water through corrosion from the plumbing materials
  • Short term exposure to high levels of copper can cause GI distress, long term may cause liver or kidney damage

Radiological Contaminants

Radiological contaminants can be natural or come from man made sources such as X-rays. Below are the most common contaminants.


  • Naturally occurring radioactive metal which occurs in low levels in virtually all rock, soil, water, plants, and animals
  • It emits alpha particles and gamma rays
  • Alpha particles are usually only harmful inside the body while gamma rays can be harmful from internal or external exposure
  • Long term exposure to radium can increase the risk of developing some severe diseases


  • Naturally occurring element found at low levels in virtually all rock, soil, and water
  • Uranium outside the body is much less harmful than if ingested inside
  • When it gets inside the body it can potentially lead to cancer or kidney damage

Unregulated Contaminants

There are some contaminants that the US EPA places on the contaminant candidate list (CCL) which states that they need more research to determine the safety and allowable levels.

These contaminants may require future regulation and they could possibly have harmful side effects when ingesting at great enough amounts now.

  • Pharmaceuticals: medicines or drugs that get in the water supply
  • Personal care products: deodorants, soap, shampoo, polish, perfumes, lotions
  • Endocrine disruptors: plastic bottles, metal food cans, detergents, flame retardants, toys, cosmetics, pesticides

How Does Water Actually Become Contaminated?

Now that we’ve gone through the common water contaminants that can cause health issues your probably wondering how exactly your water supply becomes contaminated with these substances.

In short, water becomes contaminated from the surrounding environment and byproducts from man-made agricultural and industrial processes.

Let’s learn a little more.

Water pollution

Contamination From Natural Environment

In reality, your water supply is the product of the surrounding environment.

When water precipitates to the earth gases such as carbon dioxide and oxygen enter the water from the atmosphere. The carbon dioxide can combine with water to form carbonic acid.

In areas with lots of vegetation, the oxygen in water is used and carbon dioxide is increased through the decay of vegetation.

In areas with limestone, carbonic acid and limestone interact and the water becomes hard. Calcium and magnesium bicarbonates are created which in turn makes hard water that causes scale.

In summary, when water precipatates to the surface and percolates through the ground it picks up minerals and matter from the environment causing it to change and sometimes become contaminated or impure with other substances.

Contamination From Microbes

One of the worst sources of contamination is man made activity. 

Waste from humans, farm animals, and industry plants can contribute contaminants to the water supply if not kept in check.

A few examples are excess carbon dioxide in the air from industry plants, chemical discharge from homes or plants, or improper waste treatment. 

How to Check Your Local Water Supply

To make sure your water supply does not contain large amounts of contaminants it’s important to test at least once a year and check your local water supply consumer confidence report on the EPAs website to see what the report says about contaminants.

You can also use EWGs tap water database to enter your zip code for a report.

If they show that your water supply has too much of certain contaminants then it’s best to find the correct water filter for your home. Whole house carbon filters or reverse osmosis filters can remove these contaminants effectively.


Hopefully you’re more informed about the most common water contaminants, how your water may become contaminated, and where to check to see if your water supply has too much of certain impurities.

Don’t be afraid to refer back to this guide if you need to brush up on contaminants or how to determine if you need to invest in a water filtration system for your home!