Where Does My Tap Water Come From?

Tap water is easy to take for granted. You just turn on the faucet and, voila, out comes the water. But it’s a long journey from the source to the tap. Do you know what happens along the way? What you find out might just give you good reason to start thinking seriously about home water filtration.


Source water – where tap water begins

Where does tap water come from? Tap water comes from one of two places: surface water (such as water found in reservoirs, rivers, lakes, and streams) or groundwater (water found underground in aquifers that is accessed by drilling a well). Surface water and groundwater are collectively referred to as source water.

In 2015, 61% of water used for the public supply came from surface water sources. This supplied about 87% of Americans with their drinking water. The remaining 13% of Americans supplied their own water from wells and other sources. Groundwater accounted for 98% of this self-supplied water.1

It is safe to say that no water, anywhere is free of chemicals, contaminants and toxins. All water should be filtered at some point.

Source water contamination

While on the subject of source water, it would be remiss not to take a moment to focus on water pollution. After all, this is the water that eventually becomes your drinking water. And sadly, it is most likely going to be polluted in one way or another. Just think about the news headlines today and how many different ways you hear about our water supplies being compromised—oil spills, sewage facility leaks, dumping, industrial chemical runoff, litter, exhaust, stormwater runoff carrying hazardous chemicals—the list goes on. There are also pollution sources that are relatively new to the conversation that you might not even be aware of, such as microplastics, which are showing up in our oceans and waterways at alarming rates.

Sources of water pollution are divided into 2 categories: point source and nonpoint source pollution. Point source pollution can be pinpointed to a single source, such as a chemical spill, and nonpoint source pollution comes from a nonlocalized source, such as runoff. Nonpoint source pollution is responsible for the majority of water contamination in the United States.2

Groundwater is often less contaminated than surface water because it undergoes a rudimentary type of natural filtration. For example, when rain falls, the water (carrying whatever myriad of pollutants that are picked up as the water runs off) is filtered to some extent as it travels through layers of rock, sand, and other sediment as it makes it way down to an aquifer. Surface water, on the other hand, is subject to much greater contamination because it is not subject to this type of natural filtration.


Sources of contamination

How does you tap water become contaminanted 

Natural environment

Some contamination occurs as a result of natural elements seeping into source water. For example, dangerous radioactive materials and heavy metals that are naturally a part of soil and rocks can find their way into both surface water and groundwater. While these types of contaminants are natural to the environment, they can also end up in source water as a result of mining, agriculture, and development.



Agriculture is a major source of water pollution in the U.S. Each year, farmers use over 20 million tons of chemical fertilizer on their crops and farmland, which can end up in both surface water and groundwater as a result of runoff.3

Waste (aka, manure) from agricultural livestock is another major contributor of agricultural contamination. Annually, livestock produce upwards of 1 billion tons of manure. This leaves a host of disease-causing agents in runoff that finds its way to source water.



Industry is a gross offender of source water contamination. In 2015, 190 million pounds of toxic chemicals were released into surface water by industry and business.4



Wastewater, meaning any water that has been used (such as from sinks, showers, toilets, industry, and agriculture), and stormwater runoff contain a vast number of contaminants. These can include prescription medications, human hormones, antimicrobials, pesticides, gasoline, heavy metals, toxic sludge, flame retardants, road salts, oil, just to name a few.


Water treatment

Clearly, source water that is turned into drinking water is grossly contaminated. As a result, water utilities treat source water to try and reduce remove harmful and disease-causing agents before sending it through water distribution systems that bring water to the tap. There are over 151,000 of these public water systems in the United States. The public drinking water systems regulated by the EPA provide drinking water to 90% of Americans.

Public drinking water systems use various processes to treat water that is drawn from surface water and groundwater sources to provide safe drinking water for their communities. The most common steps in water treatment include:

Step 1: Flocculation

During this step, positively-charged chemicals are added to the water. The positive charge of these chemicals neutralizes the negative charge of dirt and other dissolved particles. When this happens, the particles bind with the chemicals and form larger particles, called floc.

Step 2: Sedimentation

After flocculation comes sedimentation. In this step, floc, which is heavier than clear water, settles to the bottom of the water supply.

Step 3: Filtration

Next, the water undergoes filtration. Once the floc has settled to the bottom, the clear water on top is filtered through various (such as sand, gravel, and charcoal) to remove dust, parasites, bacteria, viruses, chemicals, and other dissolved particles.

Step 4: Disinfection

Finally, the water is disinfected with chlorine, chloramine, or another disinfectant to kill any remaining parasites, bacteria, and viruses. Disinfection also protects the water from germs it may encounter as it travels through pipes to the tap.


Post-treatment contamination

While water treatment efforts are certainly well-intended, they are in no way able to control all types of contamination. In some cases, the treatment processes actually create new contaminants. Consider the following:

  • While disinfection is a necessity for providing safe drinking water, it also poses a problem. That’s because disinfectants create harmful chemical byproducts when they come in contact with organic materials (such as those found in agricultural waste). Trihalomethanes (TTHM) and haloacetic acids (HAA) are two of these common disinfection byproducts, both of which are considered possible carcinogens
  • Many contaminants that are known to be harmful, including pesticides used in agriculture and industrial chemicals, have no legal limits, which means there is no way to know if the amount of that contaminant in water is safe
  • There are thousands of emerging contaminants being watched by the EPA because of their suspected harm, but that are not yet regulated so water utilities are not doing anything to control them 
  • Despite expensive efforts by utilities to remove agricultural and industrial contaminants, they are still found in the drinking water for millions of Americans each year
  • According to the EPA, over 850 billion gallons of untreated wastewater is released every year by sewage treatment systems5
  • Lead can leach into water on its way to the tap, even after being removed by a public water system


Water distribution

Water distribution systems are ultimately what deliver water to your tap. These distribution systems in the U.S. span almost 1 million miles and consist of pipes, valves, storage facilities, and components that transport drinking water to the public. Main distribution system lines carry water from:

  • The treatment plant to the tap
  • The source to the tap when the water is not treated

As you might suspect, water tanks and pipes, including both the pipes that carry water to homes and the pipes in homes, can cause drinking water contamination from lead, copper, and plastic.

Lead can enter drinking water when plumbing materials that contain lead, such as lead pipes, faucets, and fixtures, corrode or wear away. Water that has high acidity or low mineral content can make matters worse, as both of these conditions corrode pipes and fixtures. Lead services lines connecting the home to the main water line are typically the most significant source of lead contamination. These lines are more likely to be found in older cities and homes built before 1986. In homes that do not have lead service lines, the most common culprit of lead contamination results from brass or chrome-plated brass faucets and lead solder used in plumbing.

Further, as systems age, deterioration can occur due to corrosion, materials erosion, and external pressures. To rectify this and other distribution system issues, the EPA estimates that more than $600 billion in water infrastructure improvements are needed over the next 20 years.6



So what’s in your tap water?

With so many sources of potential contamination between source water and the water that runs freely from you tap, you might be curious to know what exactly is in your drinking water. Since 1999, all water utilities have been required by the EPA to provide a Consumer Confidence Report (CCR) for this very purpose. A CCR provides information about your community's drinking water source, the treatment your water undergoes, and any contaminants that have been detected. The intent of a CCR is to help you understand what’s in your water, so you can make an informed decision about the type of drinking water is being provided to you and your family by your local public utility.

If you are curious about what’s in your water, a CCR is a good place to start. But proceed with caution—the CCR only tells part of the story. There are many harmful substances that could be in your water but that don’t have to be legally monitored or reported on, so they won’t be anywhere on a CCR. These emerging contaminants pose a threat to your health and are good reason to consider filtering your tap water, despite what your CCR might reveal. The good news is, you have options when it comes to home water filtration and can take action to transform what out of your tap into clean and safe drinking water. 



1. USGS. Summary of Estimated Water Use in the United States in 2015.  https://pubs.usgs.gov/fs/2018/3035/fs20183035.pdf. Accessed March 2, 2020.

2. Environmental Protection Agency. Basic information about nonpoint source (NPS) pollution. https://www.epa.gov/nps/basic-information-about-nonpoint-source-nps-pollution. Accessed February 28, 2020.

3. Environmental Protection Agency. Report on the Environment. Fertilizer Applied for Agricultural Purposes. https://cfpub.epa.gov/roe/indicator.cfm?i=55. Accessed February 28, 2020.

4. Environmental Protection Agency. Toxic Release Inventory National Analysis 2015: Introduction. https://www.epa.gov/sites/production/files/2017-01/documents/tri_na_2015_complete_english.pdf. Accessed February 28, 2020.

5. Environmental Protection Agency. Report to Congress on Impacts and Control of Combined Sewer Overflows and Sanitary Sewer Overflows. https://www.epa.gov/sites/production/files/2015-10/documents/csosso_rtc_factsheet.pdf. Accessed February 28, 2020.

6. Environmental Protection Agency. About the Water Infrastructure and Resiliency Finance Center. Available at www.epa.gov/waterfinancecenter/about-water-infrastructure-and-resiliency-finance-center#create. Accessed February 28, 2020.

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