Can You Get Sick From Swimming in a Pool?

Yes, you can get sick from swimming in a pool, though it is uncommon in properly sanitized water. The illnesses that spread in pools are grouped as recreational water illnesses, ranging from diarrheal infections to ear, skin and eye problems.

Nearly all are prevented by the same two things: free chlorine held at 1 to 4 ppm and pH between 7.2 and 7.8.

What people actually catch

Diarrheal illness is the most common category. Germs like Cryptosporidium, Giardia, E. coli and norovirus enter through fecal contamination, usually from trace amounts on skin rather than a visible accident. Swallowing a small amount of contaminated water can be enough.

Swimmer’s ear is a bacterial infection of the ear canal caused by water sitting in the ear, and is more about drying out than water quality. Skin issues include hot tub rash from Pseudomonas, which thrives in warm water where sanitizer has dropped.

Respiratory irritation generally comes from chloramines rather than germs. Legionella can grow in warm water systems such as spas and cause a serious lung infection, so warm under-sanitized spa water carries more risk than a properly chlorinated pool.

If anyone develops diarrhea, a rash, ear pain, fever or breathing trouble after swimming, see a doctor and mention the pool exposure.

Why chlorine does not catch everything instantly

Chlorine kills most germs within minutes at proper levels, but not all at the same speed. Cryptosporidium has a tough outer shell and can survive in properly chlorinated water for days, which is why a diarrheal accident is a serious event and not a quick scoop and carry on.

Chlorine also only works if the rest of the chemistry cooperates. At high pH, much of your free chlorine converts to a weak form that barely sanitizes, so a pool reading 3 ppm at pH 8.2 is far less protected than one reading 2 ppm at pH 7.5. Very high cyanuric acid slows chlorine as well, stretching kill times even with normal-looking readings.

Keeping a home pool from making people sick

• Test free chlorine and pH at least twice a week, and before any gathering.
• Never let free chlorine sit at zero, even for a day.
• Shock regularly to break down chloramines and clear organic load.
• Keep the filter clean and run the pump for a full turnover daily.
• Keep water clear enough to see the main drain sharply.
• Shower briefly before getting in and never swallow pool water.
• Keep anyone with diarrhea out, and for two weeks after diarrhea caused by Crypto.
• Use swim diapers and take young children on scheduled bathroom breaks.
• Change out of a wet swimsuit promptly, since sitting in one invites rash.

Add one product at a time. Never mix chlorine with acid, and never mix different chlorine types, because either can release toxic chlorine gas. Always add chemicals to water, never water to chemicals.

After a contamination event

If there is a fecal, vomit or blood incident, get everyone out immediately. Remove solid material with a dedicated scoop, then shock and hold an elevated chlorine level for the contact time appropriate to the incident. A formed stool incident is far lower risk than a diarrheal one, which needs a long hyperchlorination period. Do not reopen until free chlorine is below 4 ppm and the water is clear.

The Key West angle

Warm water is the local complication. Our pools rarely drop into a temperature range where germ growth slows, and warm water burns through chlorine faster, so a Keys pool can go from adequately sanitized to unprotected in a couple of days in summer.

Vacation rentals concentrate the risk. Many guests, often including small children, use a pool serviced on a schedule rather than after each group, and heavy bather loads consume sanitizer quickly. Attached spas deserve extra attention, since warm water plus low sanitizer is where hot tub rash and Legionella risk live. If your pool is classed as public or commercial, confirm inspection and testing requirements with Monroe County health authorities.

Test before people swim rather than after, and treat a zero chlorine reading as a closed pool until it is corrected.