Stinky Water: Your Odor Guide

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Whether it stinks like rotten eggs or bleach, smelly water might have you worried.

The exact cause of water odors can be challenging to determine. Therefore, we have created a handy guide to help you identify and treat common causes of household water smells.

Locating the Source:

The first step to solving a smelly water problem is determining where the smell is coming from. Here’s a chart that can help you locate potential sources:



Common Water Odors and Ways to Fix Them:

Bleach, Chlorine, or Medicinal Odor

Chlorine is used by most public water suppliers to prevent bacterial growth. When added to a well (via shock chlorination) or plumbing system, chlorine produces a strong bleach odor. The best way to eliminate the smell is turn on your faucets (preferably outdoors) and let the water run until the smell is gone. In some cases, chlorine interacts with organic materials that have accumulated in your plumbing system, which increase the musty-bleach smell.

If you get your water from a well, we recommend having your water system flushed. If your water comes from a public water supply, you should contact your water supply authority.

Rotten Eggs or Decayed Odor

Generally, a sewage-like or rotten egg odor in your tap water results when sulfur-reducing bacteria grow in your drain, water heater, or well. These bacteria, which use sulfur as an energy source, chemically change the natural sulfates in water into hydrogen sulfide-which emits a distinct rotten egg odor.

Tap Score includes an option for home testing of sulfur-reducing bacteria.

Bacterial growth in the drain:

This is the most common cause for these types of odors. When organic matter (hair, soap, food waste etc.) accumulate in the drain, bacteria can thrive and produce gas that smells like rotten eggs.

Steps you can take to address this problem include:

  1. Making sure bacteria growth in the drain is the issue: Ensure that you notice a smell from one faucet when both the cold and hot water smell, and that the smell is not coming out of all faucets. Then, fill a glass with water from the faucet that does smell and step away from the sink so you can't smell any residual odor from the tap. Swirl water inside the glass a few times. Wait 30 seconds–and if the glass no longer smells, then this test suggests you likely have bacteria in the drain causing the smell.
  2. Steps to take if test if step 1 indicates the issue is bacteria growth: If the water in the glass does not have an odor, the best plan of action is to disinfect and flush the drain.

Bacterial growth in your water heater:

When hot water goes unused, bacteria in your water heater can produce a rotten egg or sewage-like smell. This occurs if your water heater is turned off for a significant amount of time or if the thermostat on the heater is set too low. These bacteria are generally not a health threat.

Fix this problem by:

  1. Making sure bacteria growth in the water heater is the issue: Confirming that your hot water smells, but your cold water does not. This generally means that the smell originates from the magnesium heating rod in your hot water tank.
  2. Steps to take if step 1 indicates the issue is bacteria growth: Call a plumber to replace your magnesium heating rod with an alternative, like an aluminum rod.

Bacterial growth at the source :

If none of the above steps lead to an answer, the odor may be from your water source itself. If this is the case, do not use or drink the water until you confirm the issue because it may contain harmful bacteria.

Private well? We recommend:

  1. Treating your well with shock chlorination because the natural chemistry of your groundwater may be supporting bacterial growth.
  2. Contacting your local health department in case a defective or improperly located septic system is located near your property.

Public water? You can address the issue by:

  1. Contacting your water supply authority or county health department
  2. Try to identify if your water source has been switched or if algal blooms have affected your water system’s water supply.

Musty, Moldy, Earthy, Grassy or Fishy Odor

When your water smells this way it is very likely that bacteria is present. Reasons your water may smell moldy include:

Decaying matter in your drain:

This is the most common cause for moldy smelling water. The best way to combat decaying matter in your drain is to disinfect, clean, and flush your drain.

Private well? Well water pollution from surface drainage:

Moldy water can be attributed to certain types of algae, fungi, or bacteria growing in your water supply–particularly during warm weather. We recommend treating your well with shock chlorination. If the problem persists, you may want to install an activated carbon filter or an automatic chlorinator (followed by an activated carbon filter).

Public water? Insufficient chlorine:

If you are on a public water supply, certain types of bacteria may grow in your supply line if an insufficient amount of chlorine is added. If you suspect this is the case, contact your water supply authority.

Petroleum or Gasoline-like Odor

These odors are rare, but could be very serious. If you are on a public water supply, contact both your water supplier and county health department immediately. Fuel-like odors may be due to:

  1. A leaking underground fuel storage tank near your well
  2. Contamination due to discharge from factories landfills
  3. Runoff from agriculture leaching into your water supply

If any of these are the case, stop drinking the water, as it may have adverse health effects, including:

  1. Anemia
  2. Increased risk of cancer
  3.  Liver and kidney problems.