Ultimate Guide to Well Water Contaminants

As a well owner, your understanding of well water contamination—and how to spot it—can help keep your drinking water safe. Even seemingly harmless changes to water quality usually means something is getting into your well water that wasn’t there before.

In this well owners' guide, we’ll go over both the common well contaminants and the sense-based signs—like cloudiness or weird smells and tastes—to help guide you to a better understanding of well contamination and what you can do about it.

Table of Contents:

• Why Clear Well Water Isn’t Always Safe
• What Are the Most Common Well Water Contaminants?
• How to Spot Well Water Contamination
• What Can I Do About Contaminated Well Water?
• Protecting Your Well
• What’s the Takeaway?

Why Clear Well Water Isn’t Always Safe

Even if your well water smells, tastes, and appears normal, that doesn’t necessarily mean it’s safe. Many pollutants are totally undetectable by our senses—including some of the biggest hazards to our health. Lead, E. coli, and arsenic, for example, are dangerous contaminants that can lurk in clear, normal smelling and tasting water.

Well Water Is Not Regulated

In the absence of regulation—which upholds the monitoring and treatment infrastructure of water utilities—well water quality is your responsibility. That’s why testing your water with a laboratory is crucial. Testing your water (just as the utilities do) is the only way to ensure you know exactly what's in your drinking water. 

Tap Score tests include reports that make recommendations using health-based guidelines, taking into account both the EPA’s Maximum Contaminant Level Goals (MCLGs) and independent studies.

How Often Should I Test My Well Water?

The EPA recommends you test your well water annually. This gives you an easily approachable routine and allows you to compare your results with some consistency. 

Extenuating Circumstances: You should test your well water any time you notice a drastic change in taste, odor, or smell, and/or anytime there is a natural or industrial disaster in your area.

Testing Your Well Water—Lab Tests vs Test Strips

Only certified laboratory testing can provide the precise and detailed analysis you require to make the right choices.

DIY test strips are really only useful for a few items, like your water’s pH levels. Many contaminants have very low detection limits that require highly specialized equipment to analyze. Color gradients, on the other hand, can be an imprecise way to determine whether or not a hazardous contaminant in your water poses a serious health risk.

 

How Do I Test My Well Water in a Lab goes into this in more detail.

What Are the Most Important Contaminants to Test for in My Well Water?

Many contaminants depend on where you live—the local geology, your proximity to things like heavy industry or agriculture, etc. Some of the contaminants that may be most important to test for in your well include:

• Bacteria (e.g., E. coli, iron bacteria, and sulfur bacteria) 
• Nitrates and nitrites
• Heavy metals (e.g., iron, lead, and arsenic)
• Radionuclides

General Well Water Parameters

It’s also incredibly important to keep an eye on basic water quality parameters, which can cause or indicate other problems if they get out of whack. These include:

• pH—can play a big role in the longevity of your plumbing and, depending on pipe material, the safety of your drinking water
• Total dissolved solids (TDS)—do not have a direct effect on your health, and may only result in technical and aesthetic issues; extremely high TDS levels (>500-1000 PPM), however, can indicate the presence of potentially harmful contaminants
• Hardness—while not a health hazard, high hardness can cause issues with your pipes, faucets, and other water fixtures, and dry out your scalp and hair
• Turbidity—refers to the clarity or cloudiness of your water, including suspended solids, like sediment and silt, and colored organic compounds, like humic substances

All Tap Score kits include a full panel of water parameters in your test.

Regional Groundwater Contaminants

Your well may be at risk of contamination by these compounds due to the natural geology of your region. The vast majority of wells draw from aquifers, a subterranean body of rock and sediment that is saturated with water that moves in, through, and around it. As a result, you may encounter higher than desired levels of:

• Radon
• Arsenic
• Uranium
• Fluoride
• Manganese
• Hardness

For example, radon is more prevalent in granitic rock aquifers than other types of aquifers. Arsenic, on the other hand, is more prevalent in areas with volcanic and granitic rock aquifers, like in the Southwest.[3]

It’s important to learn about the regional risks to your groundwater when acquiring a property with a well. Be sure to contact your local health or environmental health department to discuss any local contaminants of concern.

Our extended well core kit is the best well water test—it’s the one-stop shop for a comprehensive portrait of your well water quality, including radioactive particles like radon:

If you want to focus on radioactive particles alone, specifically alpha particles like uranium and radon:

Contaminants Near Agriculture and Heavy Industry

These contaminants end up polluting groundwater supplies via runoff or the dumping of contaminated wastewater streams into water sources by manufacturers, processing plants, and factory farms. Common chemicals and contaminants associated with industrial activity include:

• Heavy metals—like lead, arsenic, chromium, mercury, cadmium
• Pesticides
• VOCs—including those associated with petroleum products like BTEX (benzene, toluene, ethylbenzene, xylene) and MTBE
• Emerging contaminants—like PFAS and pharmaceuticals, which are often found in biosolid fertilizer
• Nitrates
• Coliform bacteria

If you live near large factory farms, we’ve done a deep dive on how agriculture pollutes private wells.

How Does Fracking Contaminate Drinking Water Wells? Hydraulic fracturing for natural gas deposits, or “fracking,” can potentially contaminate drinking water if the chemicals used to fracture rocks or the wastewater produced by the fracking process seep into nearby groundwater sources.

Nevertheless, it is complicated to examine fracking-related groundwater contamination, as the compounds used vary widely and many of them are not commonly analyzed in commercial labs or not publicly disclosed.

Well Contamination from Natural Disasters

Natural disasters can wreak havoc on your well. It is important to consider all water after a natural disaster (e.g. flood, wildfire, hurricane, etc.) unsafe until it is explicitly deemed otherwise—either by local authorities or the results of a water test. Contaminants associated with these disasters include:

• Pathogenic bacteria
• Increased nitrate concentrations
• Various organic contaminants, including VOCs

The Hidden Dangers of Floods
How Wildfires Impact Water Quality

When Can Well Water Make You Sick?

Apart from a natural disaster or an industrial or chemical spill, the most likely way your well water can make you sick is through coliform bacteria contamination. Acute symptoms include fever, diarrhea, vomiting, cramps, and nausea.

There are ways to spot contamination using your senses, which we’ll cover below. However, it is not always possible to tell that a well has been contaminated with something that cannot be picked up by our senses.

Long-term exposure to contaminants that cannot be seen, smelled, or tasted can result in health problems down the line. Add to that, water quality is complex and ever-changing. That is precisely why testing and inspecting your well annually is so important.

How To Spot Well Water Contamination

While many contaminants are undetectable, well water contamination can also leave clear signs, like changes to your water’s color, odor, and taste.

Color

Why Is My Well Water Yellow, Orange or Rusty Reddish-Brown?

Orange, red, or brown water can be caused by elevated levels of:

• Iron
• Manganese
• Iron bacteria

Iron is often accompanied by manganese and they occur naturally in groundwater. Mining nearby can raise levels of these metals in local water supplies. While low concentrations of iron and manganese are not necessarily harmful to your health, long term exposure to high levels of manganese can cause health issues. Additionally, iron, manganese, and iron bacteria can indicate or lead to other hazards. Signs of corrosion can be a serious health risk if your plumbing contains lead.

Iron bacteria naturally occur in groundwater and feed on iron. They can be identified by a buildup of red or brown slime, known as a “biofilm,” and can change the color of your water.

Why Is My Well Water Blue or Green?

Copper is the most common culprit for turning water blue or green and leaving bluish-green stains on fixtures. Copper can contaminate your water supply when corrosive water dissolves the metal in your plumbing (if your plumbing includes copper). Again, signs of corrosion can be a serious health risk if your plumbing contains lead.

While low concentrations of copper can often be found in surface and groundwater sources and are not a health hazard, at high levels (which are uncommon in drinking water) copper can cause digestive distress—like nausea, vomiting, diarrhea and stomach cramps—especially for children. Mining, farming, manufacturing operations, and industrial wastewater can also cause elevated copper levels in drinking water sources.

Why Is My Well Water Milky or Cloudy?

Cloudy water can be a sign of: 

• Dissolved air (air bubbles)
• Sediment
• Dissolved methane gas

Sediment alone may not be a health risk, but it is an indicator of a potential problem (like a loose catchment) that requires additional testing and maintenance. Sediment can introduce other pollutants and pathogens to your water supply and potentially damage or clog plumbing, pumps, and water appliances.

Dissolved methane gas in your well water can cause cloudiness as it forms bubbles when drawn from a tap. Methane may naturally occur in well water or can leak from nearby gas well drilling and landfills. Methane itself is nontoxic but can cause a hazard when released into indoor air, decreasing the levels of oxygen and, in extreme situations, causing a fire hazard (high concentrations of methane are flammable). If your well water has high concentrations of methane, cease use, make sure the area is well ventilated, and seek professional advice.

Why Is My Well Water Oily?

Iron bacteria can leave behind an oily film or sheen, particularly if the film breaks up into pieces if you stir it in a glass. Otherwise, oily sheens may be caused by contamination from petroleum products and will be accompanied by a petroleum odor. Water with petroleum contamination is unsafe to drink.

What Causes Brown or Black Gunk on Fixtures?

Brown or black gunk on fixtures is often due to a buildup of bacteria that feed on iron or manganese. These bacteria are harmless, but the gunk can build up in other places and even clog wells. They can also cause unpleasant tastes and odors, and leave behind an oily sheen. Lastly, in some cases, these bacteria can create conditions that allow other, harmful bacteria to thrive.

When excessive iron bacteria (which feed on both iron and manganese) are present, the well may require shock chlorination and filtration or other treatment processes, as well as continued monitoring as these bacteria are often difficult to eradicate.

What Causes White Residue on Fixtures?

Hard water—caused by high concentrations of calcium and/or magnesium—leaves white, chalky spots on fixtures and dishes and can cause scaling. Water with very high hardness is typically sourced from limestone aquifers. 

Hard water doesn’t generally cause any health risks, but scaling can damage your pipes, heating elements, and home appliances (like dishwashers and washing machines).

 

Smell

Why Does My Well Water Smell Like Rotten Eggs?

The trademark “rotten egg” smell is usually caused by hydrogen sulfide gas (H₂S) and/or related sulfur bacteria. Hydrogen sulfide is essentially harmless, unless it reaches very high levels in enclosed and unventilated spaces.

Left unchecked, hydrogen sulfide is corrosive to iron, steel, copper, and brass and may dissolve metals in the plumbing into your drinking water.

Why Does My Well Water Smell Like Fish?

Fishy odors can be caused by algae and/or bacteria.

Algal blooms (which are caused by an excess growth of cyanotoxin-producing cyanobacteria) can pollute surface waters (like lakes, rivers, and streams). 

Learn more about algal blooms.

Why Does My Well Water Smell Moldy or Earthy?

Moldy and earthy smells are more common—and pungent—in warm weather and are likely caused by algae, fungi, or bacteria growing in your water supply. While not all bacteria and fungi are harmful to human health, we don’t recommend taking any risks with algae, fungi, or bacteria. Consider treatment right away.

Why Does My Well Water Smell or Taste Like Chemicals, Turpentine, or Gas?

Chemical smells and tastes in water are often caused by the presence of volatile organic compounds (VOCs). VOCs are chemical compounds that are commonly used in pesticides, solvents, fuels, paints, and degreasers. They can present a range of health risks depending on the compound.

A more turpentine or gasoline-like taste or odor may indicate that there is methyl tert-butyl ether (MTBE) in your water. BTEX compounds—benzene, toluene, ethylbenzene, xylene—can also emit sweet, solvent, or fuel-like odors in drinking water. These odors may indicate leaking underground fuel storage tanks and the problem should be addressed immediately (cease use and contact a local official). 

Long term exposure to low levels of MTBE and BTEX compounds has been shown to cause a variety of potential health problems, including an increased risk of cancer for certain compounds.

 

Taste

Why Does My Well Water Taste Moldy or Earthy?

Water may taste moldy or earthy due to the presence of algae, bacteria or fungi. See the sections above for additional information.

Why Does My Well Water Taste Salty?

Salty tasting well water is usually caused by elevated total dissolved solids (TDS) levels. Most minerals that contribute to the total dissolved solids content of water occur naturally. Wells can also reach elevated levels due to contamination from road de-icing, sewage, industrial waste, and gas well drilling. 

Sulfates, which occur naturally in groundwater, can also cause salty-tasting water. High sulfates levels can cause diarrhea and dehydration, especially for infants or individuals not used to drinking sulfates.

Why Does My Well Water Taste Bitter or Medicinal?

High copper levels can cause bitter-tasting water. See more on copper above.

Why Does My Well Water Taste Metallic?

Metallic tasting water usually indicates an elevated amount of dissolved metals in your well water. These include iron, manganese, zinc, and copper. Often, this can indicate corrosion in your plumbing system, which can be a serious health risk if your plumbing contains lead.

What Can I Do About Contaminated Well Water?

If your water test shows you have contaminants in your well water, there are a number of options available to you.

What Types of Water Treatment Technologies Are Available for Wells?

You can divide treatment technologies into two basic types:

• Point-of-entry (POE), or filtration systems that treat the water as it enters the home
• Point-of-use (POU), or filtration systems that treat the water at the faucet or countertop

How Do I Know What Type of Water Treatment I Need?

The most effective way to find out is to have your water tested by a certified lab. That way you’ll get a complete picture of contaminants in your water so you can better identify the treatment system that’s right for your needs.

Once your water test points out what contaminants you should be concerned about, you'll want to learn what NSF/ANSI certifications (if any) apply.

For example, NSF/ANSI standard 53 includes lead, arsenic, VOCs, and PFAS/PFOS. You'll want to be sure the treatment device is certified to the standard for the contaminant in question. NSF/ANSI standard 58 pertains to reverse osmosis (RO) systems, but again, in a contaminant-by-contaminant basis. 

Should I Treat My Water at the Tap or the Whole House?

Again, that answer has a lot to do with the types of contaminants affecting your water. Personal preference and budget also play a large part. Once you know what's in your water you can pick the right treatment system. You can show your lab report to your local water treatment vendor. We recommend trying multiple vendors to best gauge the right price for your setup. 

Protecting Your Well Water

The best way to keep your well water safe for years to come is to be diligent and follow a well maintenance calendar. A little upkeep and maintenance (and that includes a testing regimen) goes a long way. 

Consider this Ultimate Guide to Well Owner Maintenance

What’s the Takeaway?

• Clear well water doesn’t necessarily mean it’s safe. While many water quality issues can be identified by color, taste, or odor, many pollutants are totally undetectable by our senses—including some of the biggest hazards to our health like lead, E. coli, and arsenic. Additionally, well water isn’t regulated, which leaves all the quality issues up to you. That’s why testing your well water is so important.
  

• The most important contaminants to test for in your well water are:
• Bacteria (e.g., E. coli, iron bacteria, and sulfur bacteria)
• Nitrates and nitrites
• Heavy metals (e.g., iron, lead, and arsenic)
• Radionuclides

• If your water test shows you have contaminants in your well water, you can opt for a whole-home (POE) treatment system, or a localized, point-of-use (POU) treatment system. The best treatment system for you balances your budget, your water use needs, and your water’s contaminant profile.