What Contaminants Are In Your Tap Water?

The United States Environmental Protection Agency (EPA) has 6 categories in the National Primary Drinking Water Regulations (NPDWR). These regulations protect public health by setting enforceable limits on over 90 contaminants. 

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Most states set and enforce their own drinking water regulations, which must be at least as strict as those set by the EPA. And all public water suppliers are required to provide an annual Consumer Confidence Report. So if you get your water from your city, It’s worth taking a few minutes and looking at your water report online. Keep in mind that your water quality may change between the time it leaves the treatment facility and it arrives at your tap, so it’s also important to occasionally test your tap water directly from your faucet, especially if you’ve had plumbing repairs done recently. Replacing or repairing old service lines and pipes in your home can cause a temporary increase in contaminants in your water like sediment which may include lead or other contaminants. Also, clean your aerators regularly and after any plumbing repairs to help keep contaminants out of your tap water.

What are contaminants

In the most general sense, a water contaminant is anything that isn’t a water molecule. Even minerals in drinking water are technically contaminants. But in moderation, they can be healthy for the body and improve the taste of the water. So not all contaminants are bad and any safe drinking water can be expected to have at least a small amount of contaminants. But some contaminants are unsafe at certain levels and that is why we have regulations to monitor and enforce limits on harmful contaminants. Let’s look at these broad categories of contaminants that you may find on your city’s water report. 


Microorganisms include bacteria, viruses, and parasites. Some of them are beneficial to people, but the ones that can cause illness are called pathogens. Some water pathogens will commonly cause vomiting and diarrhea but can cause skin, eye, and lung infections as well. Your local water report may show tests for coliform bacteria, which live in the environment and in the intestines of humans and animals. Not all coliform bacteria are pathogens, but coliforms are used as an indicator of potential pathogens in the water. Most of the pathogens that get into our water supplies come from animal or human waste. Some examples of pathogens that can contaminate our drinking water are:

  • Salmonella – a coliform bacteria from animal and human waste
  • E. coli 0157 – another coliform bacteria usually from cattle
  • Enterovirus – a virus usually from infected human waste
  • Giardia – a parasite from infected human or animal waste

These are just a few examples. Many more microorganisms can contaminate our drinking water, but the good news is that they can be removed from drinking water through the process of disinfection.


Modern water disinfection processes serious illnesses like cholera and dysentery. Several disinfectants are approved by the EPA to treat water:

  • Chlorine – chlorine, or hypochlorite, is the most common water disinfectant. Its been in use for over 100 years and its effective against most microorganisms. However, some people do not like the taste and smell of it in their drinking water, and when it comes in contact with Natural Organic Materials (NOM), it forms disinfection byproducts (DBPs).
  • Chloramines – chloramines, a combination of chlorine and ammonia, is the second most common water disinfectant. Chloramines have less effect on the taste of water and it forms fewer DBPs. However, it is less effective against microorganisms. 
  • Chlorine dioxide – this is more effective against microorganisms than chlorine or chloramines, affects taste less, and forms fewer of some types of disinfection byproducts. However, it requires frequent monitoring, costs more to use, and forms other types of DBPs.
  • Ozone – produced by electrical discharge, ozone is a more effective disinfectant than chlorine dioxide. It is much less commonly used because it requires more technical skill and, unlike the previous disinfectants, it offers no residual protection. It also forms other DBPs.
  • Ultraviolet (UV) radiation – UV radiation uses no chemicals, doesn’t form DBPs, and is highly effective against parasites and bacteria. However, its effectiveness can be limited by solids in the water, it’s less effective against viruses, and it provides no residual protection.

Each disinfectant has pros and cons and some water treatment facilities may use more than one type. But a common theme for most of them is that they do form DBPs as they disinfect the water, which brings up the next category of contaminants. Disinfectants can be removed by activated carbon filtration.

Disinfection Byproducts (DBPs)

Another type of contaminant resulting from the disinfection process is DBPs. These form when disinfectants come in contact with Natural Organic Materials (NOM) in the water. All surface water on the planet contains NOM, which is a carbon-based material. It mostly comes from the decay of plants and animals, but also includes bacteria. There are hundreds of types of organic compounds found in water and they all react with the different disinfectants differently to form unique DBPs. Not all DBPs are regulated or even classified, but they can be toxic at high levels. The balancing act of using enough disinfectant while keeping DBPs low is complicated by fluctuating levels of NOM due to seasonal changes and climate extremes. Chlorine, the most common water disinfectant worldwide, will produce such DBPs as:

  • Trihalomethanes (THMs) – including chloroform and bromodichloromethane 
  • Haloacetic acids (HAAs) – including bromochloroacetic acid and chlorodibromoacetic acid
  • Chlorate
  • Chlorite
  • Bromate

DBPs can be removed by reverse osmosis or activated carbon filtration

Inorganic Chemicals

Inorganic chemical contaminants in drinking water are usually minerals like iron, calcium, and zinc that have dissolved in the water. It also includes other natural metals like lead and mercury. And it also includes human-derived minerals from mining and agriculture. Inorganic chemicals affect the hardness and taste of your water. Some, like lead, can be toxic. These chemicals are not biodegradable and remain in the water until they are removed by ion exchange, filtration, or reverse osmosis.

Organic Chemicals

Organic chemicals are contaminants created by humans for a variety of industries. When not handled properly, they can contaminate water sources. Over time they can cause a variety of health issues including cancer. This includes a large number of chemicals, but the 2 main categories are volatile organic chemicals (VOCs) and synthetic organic chemicals (SOCs). Some DBPs are also VOCs. Organic chemicals can be removed by activated carbon filtering or reverse osmosis.


Radionuclides, or radioactive chemicals, may come from natural or human-derived sources, but all pose a cancer risk. Radium and polonium are 2 examples of naturally occurring radionuclides. They are found in soil and do contaminate water at low levels. Radionuclides are removed from water by ion exchange or reverse osmosis.


Hopefully, this makes you more confident when looking at your community’s water report and that you have a better understanding of the contaminants that could still be in your tap water. Additional treatment at home, such as filtration or reverse osmosis, can remove some of the residual effects of treatment.