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The Ultimate Tap Water Odor Guide

The Ultimate Tap Water Odor Guide

 

No one likes a stink—certainly not when it’s coming from your sink! Sometimes your tap water can carry odors that make you second guess your water quality. Luckily, odors are rarely a real cause for alarm.

This ultimate guide is here to answer all your odor questions, including where the stink is coming from, what it means, and how to deal with it so you can go back to trusting the quality of your tap water.

Table of Contents:

Smelly Tap Water: Where Is It Coming From?

The exact cause of smelly water can be difficult to determine. The first step toward solving your water odor issue is locating the source of the smell. Consider this guide to help locate the source of the odor:

 tap water odor source guide
We’ll explore potential causes below.

Why Does My Tap Water Smell Like Chlorine or Bleach?

Tap water from a public water supply or utility is likely treated with chlorine to prevent bacterial growth. For private wells, it is advisable to shock chlorinate to help treat water supplies, which can also cause a strong bleach odor.

Private Well Supplies

Well owners are responsible for maintaining the safety of their own water supply. Shock chlorination is the standard method of well disinfection, in which a high level of chlorine is introduced for up to 12 hours, and will leave behind a strong bleach odor unless pumped out adequately. 

Turn on your faucets and run your water until the odor of bleach dissipates. Sometimes, the chlorine will interact with built-up organic matter in the plumbing system and add to the odor. 

If you are still having issues after running your water for a few minutes, consider having your plumbing system flushed by a professional plumber or licensed well driller.

Public Water Supplies

Levels of free chlorine in public water supplies are typically between 0.5 and 2.0 PPM, although levels have been known to reach 5.0 PPM.[1] The Centers for Disease Control & Prevention (CDC) considers levels of chlorine up to 4.0 PPM to be perfectly safe in drinking water.[2

Chlorine odors should go away when exposed to air for a few minutes. Also, if taste is an issue, most standard pitcher filter devices filter out the taste of chlorine.

If the scent of chlorine does not dissipate after a few minutes, or if bathing in chlorine is having noticeable impacts on your hair and skin and you suspect something is amiss, contact your utility right away.

Visible Impacts of Water Chlorination

Disinfection Byproducts (DBPs)

Disinfection byproducts (DBPs) are a group of odorless chemical compounds that are formed when chlorine reacts with organic materials in water, as in the case of chlorinated tap water and chlorine-treated swimming pools. While chlorination is integral to maintaining healthy water systems, DBPs are a reminder that water quality is very nuanced.

In addition to drinking them, you can be exposed to DBPs by breathing them in during showering, bathing, dishwashing and swimming. Your skin can also absorb DBPs during exposure, but they only remain in the body for short periods of time. Chronic exposure to DBPs, however, has been known to increase the risk of cancer in humans.[3

Disinfection byproducts are of greatest concern to those on municipal water systems. Learning more about the level of DBPs in your water supply—among them trihalomethanes (THMs) and haloacetic acids (HAAs)—is a leading reason to have your municipal tap water tested.

You can test specifically for haloacetic acids in your water supply.

Why Does My Tap Water Smell Like Rotten Eggs?

Tap water with that sulfurous “rotten egg” smell is likely the product of sulfate-reducing bacteria, which can grow in your drain, your water heater, or your well. These bacteria use sulfur as an energy source, chemically changing natural sulfates in water into hydrogen sulfide which emits that distinct, rotten egg odor.

What Are Sulfates?

Sulfate is a compound composed of sulfur and oxygen that is almost universally present in water. Sulfate dissolves into groundwater as it passes through mineral deposits, soil, and rock formations that contain sulfate minerals. 

Waste streams from industrial activity or agricultural runoff can also contribute to sulfate in groundwater or surface water supplies. Aluminum sulfate is often used in conventional water treatment, which can contribute sulfate to drinking water.

Sulfates themselves do not produce an odor. Sulfate minerals can cause scale to build up in your pipes.

What Is Hydrogen Sulfide?

Hydrogen sulfide (H2S) is a colorless, flammable gas most known for its trademark rotten egg odor. H2S can form naturally underground as organic matter decomposes, but is most often produced by sulfate-reducing bacteria, that convert sulfates in water into hydrogen sulfide.

Sulfate-reducing bacteria live in oxygen-deficient environments (like landfills and deep wells) and can form in water treatment devices (like water softeners and water heaters). H2S (with its rotten egg odor) most commonly affects well owners. Warmer temperatures bring hydrogen sulfide odors out more intensely.

Drain, Water Heater, or Well?

    • Drain: When organic matter (hair, soap, food waste, etc.) builds up and decays in a drain, bacteria thrive and produce gasses that can include H2S and smell like rotten eggs. See the diagram above to determine whether or not your drain is the culprit. (It should only smell in one drain, both hot and cold water, and the water itself should not smell after a quick swirl.)
    • Water Heater: Water heaters that aren’t used often, have been left off for a time, or have the thermostat set too low will stimulate bacterial growth that may produce a rotten egg odor. While unpleasant, these bacteria are not health risks. 

      On the other hand, water heaters often have a component (usually a magnesium rod) that can produce a sulfide smell as it deteriorates over time. See the diagram above to isolate your water heater as a cause.
    • Well: If the source of your rotten egg smell is not your drain or water heater, bacteria could be growing at your well. We recommend ceasing use of your water until you have it tested.
      • Inadequate wellhead protection may allow surface water contamination to stimulate bacterial growth.
      • The natural groundwater in your area could be stimulating hydrogen sulfide-producing bacterial activity.
      • A defective or improperly located septic tank could be near your well.

If you’re on a public water supply and your water smells like rotten eggs (and you’ve ruled out your drain and water heater), cease use and contact your utility as soon as possible.

Is Hydrogen Sulfide in My Water Supply Dangerous?

Hydrogen sulfide (H2S) is not typically a health risk. The threshold for noticing the odor is around 1 PPM[4] and typical household concentrations rarely surpass 10 PPM. 

Inhaled at higher concentrations (>20 PPM), however, H2S causes undesirable effects, and can become highly toxic or lethal at very high concentrations (>500 PPM).[5] These concentrations are unlikely in drinking water.

It is worth mentioning that, apart from the unpleasantness of the odor, hydrogen sulfide left unmanaged in a well water supply can be corrosive to iron, steel, stainless steel, copper, and brass, leading to greater unwanted problems with your plumbing (including leaching of other harmful chemicals).

How Do You Test for Hydrogen Sulfide?

You can test for hydrogen sulfide with at-home strips to confirm its presence (although the smell is unmistakable). 

That being said, it’s important to consider a laboratory test to get an overall picture of your water quality before considering any treatment method. Hydrogen sulfide escapes from water quickly. Paying particular attention to the instructions included in a lab testing kit will help ensure the highest accuracy. 

Targeted testing for hydrogen sulfide.

How Do You Remove Hydrogen Sulfide from Tap Water?

Once you’ve determined the source of your rotten egg smell to be your well supply, shock chlorination is the recommended way to eliminate sulfate-reducing bacteria.

Why Does My Tap Water Smell Like Oil, Gasoline or Petroleum?

If your tap water smells like oil, gasoline or other petroleum products or solvents, it could be a sign of a serious problem brought on by an industrial spill or malfunction of some sort. Cease use and have your water tested right away.

Private Well Supplies

Causes of petroleum-smelling water are usually a cause for concern, although relatively rare. These odors may suggest: 

    • A fuel tank or fuel storage supply leak near your well
    • Industrial discharge from local industry or factories that has polluted the groundwater supply

It’s important to cease use at this point until your water has been tested.

Public Water Supplies 

Although mostly an issue impacting well owners due to quality control procedures present at municipal or public utilities, if you are on a public water supply and your water smells like petroleum or solvents, call and report the issue to your utility and health department right away.

Exposure to water contaminated by petrochemicals and solvents can have serious health impacts including headaches, dizziness, nausea, and vomiting. Chronic exposure can lead to more serious complications.

Iron Bacteria

It’s worth noting that iron bacteria—which can also cause an oily sheen or even a slime to appear on your water—can produce an odor sometimes considered oil or petroleum-like. The scent is usually more swampy and musty than chemical, however, and iron bacteria leave behind stains.

How to spot iron bacteria in your water supply.

Why Does My Tap Water Smell Moldy, Musty, Earthy or Fishy?

Moldy, musty, or fishy odors in your water or drain are typically the result of bacterial activity and almost always affect those on private well systems. (Mold in your drain can be an issue as well, but more on drains next.)

These odors are harmless, if unpleasant, and often caused by:

  • Built-up decaying matter in the drain
  • Well water pollution from surface drainage

The scent is almost always the product of bacterial activity. Most commonly, the issue is with your drain. But occasionally your well will run into issues that can cause your water to smell musty, grassy, or even fishy. To determine if the issue is with your drain:

  1. Fill a glass of water from the faucet in question
  2. Step away from the sink and swirl the water in your glass
  3. If the odor is no longer present, the problem is with your drain

Otherwise, well owners should pay attention to their system’s pressure tank. Periodic cleaning and maintenance of the pressure tank will prevent bacterial growth from reaching levels that cause musty or earthy odors in tap water.

Warmer weather can also stimulate the growth of certain types of algae, fungi, and bacteria, leading to stinky water. 

Once again, shock chlorination followed by a thorough draining out of the chlorine should solve your odor issues. If the problem persists, activated carbon filtration systems (pitcher, point-of-use, or point-of-entry) can help with odor and flavor. 

If for some reason musty or earthy water is coming out of your tap on a public water system and the problem isn’t your drain, call your utility right away. There may be issues with the facility’s chlorination system.

Why Does My Drain Smell?

Most of the time, your drain smells due to debris or gunk buildup that has stimulated bacterial growth. A good cleaning out and disinfecting of your drain usually solves the issue.

Gunk and Debris Buildup

Over time, organic matter like hair, food scraps, grease and other debris get caught in your drain. As the collection of debris builds up, it can block and clog your pipes. These blockages are also ideal breeding grounds for a wide range of bacteria and other microbes, which grow and emit foul odors as a byproduct.

Clogs and buildup can lead to stagnant water pooling that may attract pests like mosquitoes and cockroaches. 

How to fix: While there are chemical-based drain cleaners available at every grocery store, a DIY solution combines baking soda, vinegar, hot water to do the trick, along with a drain brush to provide assistance.

Mold and Mildew

Mold and mildew can grow from the tiniest of leaks and spread underneath your sink or inside your walls. Once the spores grow into mold, some release microbial volatile organic compounds (MVOCs) which are odorous and scatter in the air. Smells include musty, rotten, or “wet sock” smell.

For those who are more sensitive, mold and mildew can lead to unwanted health impacts including coughing, eye irritation, and stuffy nose.[6]

How to fix: Similar to gunk and debris, mold can be combated with a distilled white vinegar and hot water combo, or hydrogen peroxide paired with hot water.

Empty Drain Traps

There are a variety of waste and drain traps in homes, but they all serve to prevent sewer gasses from re-entering. Drain traps are found below or within a fixture, shaped like a u-bend or s-bend so that a small amount of water is always “trapped” within. The water acts as a shield to block unpleasant odors from making their way back up.

Hydrogen sulfide, ammonia, and methane are the most common sewer gasses.

How to fix: Empty drain traps are more common with unused or infrequently used sinks, toilets and showers. Simply pour water into every drain you can find and ventilate your space. The smells should not return.

Plumbing Issues

Mistakes during plumbing work or installation (e.g. traps or vents installed incorrectly) may allow smells to develop for a number of reasons. Leaks and deteriorating drain lines may also lead to odors.

How to fix: If your plumbing is the issue, have a professional plumber survey the situation.

Is It Safe to Drink Water that Smells?

As we covered above, the source of bad smelling water varies, and occasionally this can make water unsafe to drink. Aesthetic (smell, color, taste) changes to water don’t always pose a threat to human health. However, sudden or drastic changes to your water’s smell or appearance could indicate a larger problem. 

If locating the source of the odor is not straightforward, we recommend having your water tested before continuing to use it or seeking treatment.

Private Well Supplies 

As the owner of a private well, you are responsible for maintaining the quality and safety of your water supply. Having your water tested, at least annually, is an integral step in assuring you and your household have water that is safe to drink.

Well water that smells at the source (not at the drains, water heaters or treatment devices) should be tested and remedied before drinking.

Public Water Supplies

As a public utility customer, it’s important to know that your utility is there to communicate with you if you ever suspect something is wrong. If you experience something you’re not sure about, reach out to them.

Public water supplies typically encounter issues far less frequently than private wells. Keep an eye out after natural disasters and industrial disasters near your treatment plant, and take note if your water ever smells like petroleum, oil, or solvents.

There are also resources to help you determine possible contaminants by their smell, such as the CDC’s Agency for Toxic Substances and Disease Registry.[7]

When Should I Test My Smelly Water?

Testing your water is never a bad idea, especially when your water has undergone a sudden aesthetic change (like developing a bad odor). As we covered above, the source of bad smelling water is often not the water supply itself. That being said, if you’ve ruled out other potential causes, have your water tested.

Tap Score Essential City Water Test
Core Kit
Essential City Water Test
49 Analytes Tested
$ 169.00
Tap Score Essential Well Water Test
Core Kit
Essential Well Water Test
54 Analytes Tested
$ 199.00

Can You Filter or Treat Stinky Water?

While treatment technologies exist to remove foul odors from your water before you drink it, most of the odors we covered have a cause that, when addressed, can resolve your stinky water problems at the source. 

In particular, when dealing with plumbing or well system issues, remedying the issue will save you money and trouble down the line. Likewise if you’re on a public water system, if the issue can’t be addressed with your pipes or drains, contact your water provider—this is especially true if your neighbors are experiencing the same odor problem.

Typically, activated carbon filtration technologies, as well as reverse osmosis point-of-entry systems, help remove aesthetic issues like color, taste, and smell from your water.

Remember: Issues related to bacterial growth should always be eliminated (via shock chlorination) rather than filtered.

Where Can I Get My Water Tested?

Why Trust Tap Score?

We know how confusing it can be to find advice on water quality and treatment you can trust. That’s part of the reason we made Tap Score—to help improve the way you test and treat your drinking water.

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  • Unbiased advice: Our blog is independently researched by our team of water scientists and designed to provide clarity on water quality, not to sell treatment products.
  • Independent laboratory testing: Tap Score test results come from SimpleLab's third-party network of certified laboratories; in other words, accredited labs provide the data without conflicts of interest.
  • Continuously updated: Science never rests. That’s why our content always reflects the latest developments in scientific research and regulatory standards.
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About The Author
Sasha Sosnowski, PHD

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