A hot tub should not have a strong or unpleasant odor.
If the water smells unusually strong, sour, musty, sulfur-like, dirty or heavily chemical, do not assume the smell is normal. Odor can be a warning sign that the water chemistry, sanitation, filtration or plumbing needs attention.
A properly maintained hot tub should have little noticeable odor. So if you are asking, “Is it safe to get in my hot tub if it smells bad?”, the safest approach is to stay out until you understand what is causing the odor and confirm that the water is properly sanitized and balanced.
What Should Hot Tub Water Normally Smell Like?
A properly maintained spa may have a mild sanitizer odor, but it should not smell overpowering, foul or unusual.
Strong odors can be associated with:
- Improper sanitizer levels
- Chloramines or other disinfection byproducts
- Organic contamination
- Dirty filters
- Biofilm in the plumbing
- Old water
- Bacteria
- Source-water minerals or sulfur compounds
- Improper pH
Odor alone cannot tell you exactly what is wrong, but it is a useful warning sign that the spa should be checked before use.
Why Does My Hot Tub Smell Strongly Like Chlorine?
Many people assume a powerful chlorine smell means the water contains a lot of chlorine and therefore must be very clean.
That is often the opposite of what is happening.
When chlorine reacts with contaminants such as sweat, dirt, urine and other organic material, it can form compounds called chloramines. These compounds are commonly responsible for the strong “chlorine smell” people associate with heavily used recreational water.
Those contaminants also consume chlorine that would otherwise be available to sanitize the water.
If your spa suddenly develops a much stronger chemical smell than usual, test the water rather than assuming the sanitizer level is good.
Is A Strong Chlorine Smell Dangerous?
A strong smell does not automatically mean someone will become sick, but it should not be ignored.
Chloramines and poorly balanced water can contribute to:
- Eye irritation
- Skin irritation
- Respiratory irritation
- An unpleasant chemical odor
If the odor is strong enough to make your eyes burn, irritate your throat or make breathing uncomfortable, leave the spa and address the water condition before using it again.
Why Does My Hot Tub Smell Musty?
A musty or damp odor may indicate organic buildup, dirty filters, stagnant areas or biofilm developing somewhere in the system.
Biofilm is a layer of microorganisms and organic material that can develop on wet surfaces and inside plumbing.
Possible places to investigate include:
- Filter cartridges
- Filter housings
- Jet plumbing
- Water lines
- Under the spa cover
- Headrests and accessories
- Areas where water does not circulate well
If a musty smell persists after normal water treatment and filter cleaning, the plumbing may need a more thorough purge and cleaning.
What Does A Rotten-Egg Or Sulfur Smell Mean?
A rotten-egg odor is often associated with sulfur compounds in the source water, but it can also occur in poorly maintained or stagnant water.
If the smell appeared immediately after filling the spa, your source water may be a factor.
If it develops only after the water has been sitting in the spa for a period of time, investigate sanitation, filtration and plumbing cleanliness as well.
Do not try to mask the odor with fragrance products. Identify the cause first.
Why Does My Spa Water Smell Sour Or Dirty?
A sour, dirty-water or swamp-like smell is a strong indication that the water should be evaluated before anyone gets in.
Possible causes include:
- Low sanitizer
- Heavy bather contamination
- Dirty filters
- Old water
- Biofilm
- Organic debris
- Improper water balance
If the spa smells dirty, treating the symptom with fragrance or adding chemicals without testing the water is not enough. The underlying water-quality problem needs to be corrected.
Can Hot Tub Water Smell Because The Filter Is Dirty?
Yes.
The filter continuously collects oils, dirt, hair, skin cells and other material from the water. If it becomes heavily loaded or is not cleaned regularly, water quality can deteriorate.
A dirty filter can also reduce circulation, making it more difficult for sanitizer and filtration to keep the water clean.
If an unusual odor develops, inspect the filter.
Depending on its condition:
- Rinse it thoroughly.
- Deep clean it using an appropriate cartridge cleaner.
- Replace it if the media is damaged, heavily contaminated or beyond its service life.
Can Old Hot Tub Water Start To Smell?
Yes. Hot tub water does not last indefinitely.
Because spas contain a relatively small volume of warm water and often receive a heavy concentration of bathers compared with swimming pools, dissolved contaminants can accumulate over time.
Eventually, the water may become increasingly difficult to balance and sanitize.
Signs that a drain and refill may be appropriate include:
- Persistent odor
- Repeated cloudiness
- Foaming
- Difficulty maintaining sanitizer
- Water that feels different or uncomfortable
- Chemistry that becomes increasingly difficult to control
Can A Smelly Hot Tub Make You Sick?
The odor itself is not necessarily what causes illness. The concern is that an abnormal odor can indicate conditions that allow germs or irritating compounds to develop.
Improperly maintained hot tub water can expose bathers to organisms that may cause skin, respiratory or gastrointestinal illness.
Two well-known hot-tub-related health concerns are hot tub rash and illness associated with Legionella.
What Is Hot Tub Rash?
Hot tub rash, also called Pseudomonas folliculitis, can occur after exposure to water contaminated with Pseudomonas aeruginosa.
Symptoms may include:
- Itchy red bumps
- Red or irritated skin
- Pus-filled bumps around hair follicles
The rash may be more noticeable in areas where a swimsuit held contaminated water against the skin.
What About Legionella?
Hot tubs can also provide conditions in which Legionella bacteria can grow if sanitation and maintenance are inadequate. Because hot tubs create mist and aerosols, contaminated water can potentially be inhaled.
If you recently used a hot tub and develop symptoms such as:
- Cough
- Shortness of breath
- Fever
- Muscle aches
contact a healthcare provider and mention your recent hot tub exposure.
What Should You Test If The Spa Smells Bad?
At minimum, check:
- Free chlorine or bromine
- pH
- Water clarity
- Filter condition
- Water age
As a general reference, hot tubs should normally maintain appropriate sanitizer levels and a properly balanced pH. Follow the recommendations for your particular sanitizer system and chemical products.
What If The Sanitizer Level Is Zero?
If chlorine or bromine is depleted, do not simply get into the spa because the water still looks clear.
Sanitizer is one of the primary defenses against microorganisms in recreational water.
Contamination from bathers, organic material and normal spa use continually consumes sanitizer.
Restore the water to the appropriate sanitizer and pH range before use.
Should You Shock The Spa?
If the odor is caused by organic contamination or chloramine buildup, an appropriate oxidizing or shocking treatment may be part of the correction process.
Always follow the chemical manufacturer's instructions.
After treatment, allow the water to circulate and confirm that the sanitizer and pH are back within an appropriate range before anyone gets in.
Never mix pool or spa chemicals together and never exceed labeled dosing instructions.
When Should You Drain And Refill Instead?
A drain and refill may be the better solution when:
- The odor returns repeatedly after treatment.
- The water is old.
- The water is persistently cloudy or foamy.
- Sanitizer is difficult to maintain.
- There is suspected biofilm or major contamination.
- The spa recently experienced a fecal or serious contamination event.
For serious contamination events, see our Hot Tub Contamination Guide.
What If The Smell Is Coming From The Spa Cover?
Sometimes the water is not the only source of odor.
The underside of a spa cover is warm, damp and exposed to water vapor. Dirt, mildew or organic material can accumulate there.
Inspect:
- The underside of the cover
- Cover seams
- Headrests
- Cabinet areas
- Nearby drains and decking
A smell coming from these areas may require cleaning even if the water itself tests normally.
What If The Spa Smells Fine But The Water Is Cloudy?
Odor is only one indicator of water condition.
A spa can have little odor and still have improperly sanitized water. Likewise, clear water does not guarantee that every microorganism is absent.
That is why routine water testing is more reliable than appearance or smell alone.
Should You Use A Hotel Or Airbnb Hot Tub If It Smells Strong?
No one can determine the complete condition of a public or rental spa from smell alone, but a strong chemical or unpleasant odor is a valid reason to stop and investigate.
Before using a hotel, Airbnb or other shared hot tub, look for:
- Clear water
- No strong or unusual odor
- Clean surfaces
- Secure drain covers
- Reasonable water temperature
- Proper sanitizer and pH when testing information is available
If the spa smells unusually strong or looks poorly maintained, report the condition to the operator and stay out until it has been addressed.
When Should You Definitely Stay Out?
Do not use the hot tub until the cause is understood if:
- The smell is very strong or suddenly different.
- Your eyes or throat begin to burn.
- The water is cloudy, green or slimy.
- The surfaces feel sticky or slippery.
- The sanitizer cannot be verified.
- The spa has recently been contaminated.
- There is visible mold or biofilm.
- The water condition cannot be restored with normal maintenance.
If you are unsure about multiple warning signs, see our 15 Warning Signs To Stay Out Of A Hot Tub.
A Simple Smelly-Water Troubleshooting Order
- Stay out of the spa until you evaluate the problem.
- Test chlorine or bromine.
- Test pH.
- Inspect water clarity.
- Check and clean the filter.
- Inspect the spa for slime or biofilm.
- Determine how old the water is.
- Correct chemistry according to product instructions.
- Drain and refill if the water cannot be restored reliably.
- Confirm normal sanitizer, pH, clarity and odor before returning to use.
The Bottom Line
A hot tub should not smell strongly chemical, sour, musty, rotten or dirty.
A strong smell does not automatically tell you exactly what is wrong, but it is a warning sign worth investigating.
Test the sanitizer and pH, inspect the filter and surfaces, consider the age of the water and look for other symptoms such as cloudiness, slime or foam.
Most importantly, do not assume a powerful “chlorine smell” means the water is extra clean.
For more information about unusual water appearance, contamination, temperature, children, pets, drains, electrical hazards and other safety concerns, visit our Water Safety Knowledge Base.
If your water-quality problem appears to involve a filter, circulation pump, sanitation system or another replacement component, visit our Find My Part page or contact Bath & Spa Parts Online.