Introduction
A sewage-like smell associated with water can be unpleasant and concerning. In many cases, the smell does not actually come from the water itself. Instead, it may originate from a sink drain, floor drain, plumbing vent or other parts of the wastewater system.
In some situations, particularly with private wells, a sewage odour may indicate contamination from surface water, septic systems or other sources. Determining where the smell originates is therefore the first step in solving the problem.
Is a Sewage Smell Dangerous?
A sewage smell should never be ignored.
If the odour comes from a drain or plumbing fixture, it is often a maintenance issue rather than a drinking water problem. However, if the smell is present in the water itself, contamination may be possible and further investigation is recommended.
Potential concerns include:
- Bacterial contamination
- Surface water intrusion
- Septic system leakage
- Organic contamination
- Poor well construction or maintenance
Does the Smell Come From the Water or the Drain?
Before considering treatment equipment, determine whether the smell is actually coming from the water.
The Glass Test
Fill a clean glass with cold water and move away from the sink.
- If the smell disappears, the drain or plumbing system is usually the source.
- If the smell remains in the glass, the water itself may be affected.
- If only one tap smells, the problem is often local to that fixture.
- If every tap smells, the source may be the plumbing system, water heater or water supply.
This simple test can often save time and unnecessary expense.
Common Causes of Sewage-Like Odours
Dry Floor Drains and Water Traps
Floor drains, shower drains and sink traps contain water that blocks sewer gases.
When a drain is not used for a long period, the water may evaporate and allow sewer gases to enter the room.
Typical signs
- Smell strongest near a drain
- Unused basement or utility room drains
- Water itself smells normal
Solution
Run water into the drain to refill the trap.
Dirty Sink Drains
Food residues, grease, soap deposits, hair and biofilm can accumulate in drain pipes and overflow channels.
As these materials decompose, they may produce odours that resemble sewage.
Typical signs
- Strong smell directly at the sink
- Glass of water smells normal
- Kitchen sinks frequently affected
Solution
Clean the drain and overflow thoroughly.
Blocked or Faulty Vent Pipes
Plumbing systems use vent pipes to release sewer gases safely above the roof.
If a vent becomes blocked or damaged, odours can enter the building.
Typical signs
- Multiple fixtures affected
- Slow-draining sinks or showers
- Gurgling sounds in pipes
Solution
Inspect and repair the vent system.
Sewer Line Problems
Damaged or partially blocked sewer lines can allow sewer gases to enter a building.
Typical signs
- Persistent odours
- Multiple drains affected
- Slow drainage
- Wastewater backups
Solution
Professional inspection and repair may be required.
Sewage Smell in Private Well Water
A sewage smell that remains in a glass of water should be taken seriously, especially if the property uses a private well.
Possible causes include:
- Septic system leakage
- Surface water entering the well
- Damaged well caps
- Cracked well casings
- Flooding or heavy rainfall
- Poor drainage around the wellhead
Water testing is often recommended to determine whether contamination is present.
Bacterial Contamination
Contamination from wastewater may introduce bacteria and other microorganisms into groundwater.
Possible warning signs include:
- Sewage-like odours
- Cloudy water
- Changes in taste
- Recent flooding
- Nearby septic system problems
Recommended water tests
- Total coliform bacteria
- E. coli
- Nitrate
- General water quality parameters
If E. coli is detected, the water should be considered unsafe for drinking until the source of contamination has been identified and corrected.
Hot Water Only?
If the odour is noticeable only when using hot water, the water heater may be responsible.
Possible causes include:
- Sediment accumulation
- Bacterial growth inside the tank
- Reactions involving the anode rod
Simple check
Compare hot and cold water from the same tap.
If only the hot water smells, investigate the water heater before focusing on the well or incoming water supply.
Troubleshooting Steps
1. Determine where the smell occurs
Is the smell present:
- At one tap only?
- At every tap?
- Near drains only?
- In hot water only?
- In cold water only?
2. Perform the glass test
Move a glass of water away from the sink and smell the water directly.
This helps determine whether the odour comes from the water or the plumbing system.
3. Inspect drains
Check:
- Sink drains
- Floor drains
- Shower drains
- Utility room drains
Dry traps and organic buildup are common causes of sewage-like smells indoors.
4. Consider recent events
Have any of the following occurred recently?
- Heavy rainfall
- Flooding
- Well maintenance
- Septic system work
- Plumbing repairs
- Extended vacancy of the property
These events can sometimes explain a sudden change in water quality.
5. Test the water
If the water itself appears to smell, laboratory testing can help determine whether contamination is present and what corrective actions may be needed.
Treatment Options
The correct solution depends on what is causing the smell.
In many cases, a sewage-like odour is not caused by the water itself. The smell may come from a drain, floor trap, sewer vent or water heater. If the odour is coming from the water, the source should be identified before selecting a treatment system.
The following examples show common causes and typical solutions.
Sewage smell from a drain or plumbing system
If the smell disappears when a glass of water is moved away from the sink, the drain is often the source of the problem.
Possible solutions
- Clean the drain and overflow channel
- Refill dry floor drains and water traps
- Remove grease, soap deposits and organic buildup
- Inspect blocked or damaged vent pipes
- Repair damaged sewer pipes if necessary
Typical solution path
Drain inspection
→ Cleaning and maintenance
→ Vent inspection if required
→ Problem resolved
Water treatment equipment is normally not required.
Bacterial contamination in a private well
A sewage smell that remains in the water itself may indicate contamination from surface water, flooding, animal waste or a nearby septic system.
Typical solution path
Water analysis
→ Find the source of contamination
→ Repair the well or eliminate the contamination source
→ Disinfect the well
→ Follow-up testing
Common corrective measures
- Replace damaged well caps
- Repair casing defects
- Improve drainage around the well
- Correct septic system problems
- Shock chlorinate the well
Ongoing bacterial protection
Some private wells experience recurring bacterial problems, particularly after heavy rain or seasonal groundwater changes.
A UV system may provide additional protection.
Typical treatment system
Raw water
→ Sediment filter
→ UV disinfection
→ Distribution system
| Treatment step | Function |
|---|---|
| Sediment filter | Removes particles and protects the UV unit |
| UV disinfection | Inactivates bacteria, viruses and other microorganisms |
UV systems do not remove odours, colour, dissolved contaminants or nitrate.
Septic system contamination
If a septic system is affecting a well, the source of contamination should be corrected before treatment equipment is considered.
Typical solution path
Water analysis
→ Septic system inspection
→ Septic system repair
→ Well rehabilitation if necessary
→ Disinfection
→ Follow-up testing
Simply installing a filter will not solve an active contamination problem.
Surface water entering the well
Heavy rain, flooding or poor well construction can allow contaminated surface water to enter a well.
Typical solution path
Water analysis
→ Wellhead inspection
→ Repair construction defects
→ Improve drainage around the well
→ Disinfection
→ Follow-up testing
Common improvements
- Install a sanitary well cap
- Seal casing penetrations
- Restore damaged grout
- Raise the wellhead above surrounding ground level
- Divert rainwater away from the well
Naturally occurring organic odours
Some groundwater sources contain naturally occurring organic compounds that may produce odours resembling sewage even when no bacterial contamination is present.
Water analysis should confirm that contamination is not present before treatment is selected.
Typical treatment system
Raw water
→ Sediment filter
→ Activated carbon filter
→ Distribution system
| Treatment step | Function |
|---|---|
| Sediment filter | Removes suspended particles |
| Activated carbon | Reduces taste and odour compounds |
Activated carbon improves taste and odour but does not disinfect the water.
Municipal water with a sewage-like odour
A genuine sewage smell in a municipal water supply is uncommon.
If several neighbouring properties experience the same problem, contact the water utility before installing treatment equipment.
Typical solution path
Contact water supplier
→ Confirm water quality
→ Inspect household plumbing and drains
→ Install activated carbon filtration if required
Activated carbon filtration may help reduce unwanted taste and odour where the water supply itself complies with drinking water standards.
Which Treatment Is Appropriate?
| Cause | Typical solution |
|---|---|
| Dry floor drain or water trap | Refill trap |
| Dirty drain or overflow | Cleaning and maintenance |
| Blocked vent pipe | Plumbing repair |
| Water heater problem | Service water heater |
| Bacterial contamination | Remove source and disinfect |
| Septic contamination | Repair septic system and retest |
| Surface water intrusion | Repair well and improve drainage |
| Organic odours | Activated carbon filtration |
| Seasonal bacterial risk | Sediment filtration and UV disinfection |
| Municipal taste or odour issue | Activated carbon filtration |
Frequently Asked Questions
Why does my water smell like sewage but taste normal?
The smell often comes from a nearby drain rather than the water itself. The glass test can help determine the source.
Can a sink drain smell like contaminated water?
Yes. Organic buildup in drains and overflow channels is one of the most common causes of sewage-like odours indoors.
Should I drink water that smells like sewage?
If the odour remains in the water itself and the cause is unknown, further investigation and water testing are recommended, particularly for private wells.
Can a septic system affect a well?
Yes. Septic system failures can contaminate groundwater and affect nearby wells.
Will activated carbon remove sewage contamination?
No. Activated carbon may reduce certain odours but does not disinfect contaminated water.
Conclusion
A sewage smell associated with water is often caused by drains, plumbing fixtures or sewer gases rather than the drinking water itself. However, when the odour is present in the water, especially in private well systems, contamination should be considered as a possibility. Careful troubleshooting, water testing and corrective action can usually identify and resolve the problem while ensuring that the water remains safe to use.