Water and contact lenses do not mix, and the reason has a name: Acanthamoeba. It is a microscopic organism that lives in tap water, swimming pools, lakes, hot tubs and shower heads. It is harmless to almost everyone — unless it gets trapped between a contact lens and your cornea.
Why this one organism drives the whole rule
Acanthamoeba keratitis is rare. It is also one of the worst things that can happen to an eye.
- It is extremely painful, characteristically far more painful than the eye looks
- It is hard to diagnose early and is often mistaken for a viral or bacterial infection for weeks
- Treatment runs for months, with drops sometimes hourly around the clock
- It can end in corneal scarring, transplant, or permanent vision loss
The overwhelming majority of cases occur in contact lens wearers, and the common thread is water exposure. A lens creates exactly the conditions the organism needs: a tight, warm, low-oxygen space held against the cornea for hours.
That is why the guidance is absolute rather than proportionate. The risk per exposure is low; the consequence is severe enough that it is not worth accepting repeatedly.
Swimming
Do not swim in contact lenses. Pool chlorine does not kill Acanthamoeba at the concentrations used in swimming pools, and lakes, rivers and the sea are worse.
There is a second problem people notice faster: soft lenses absorb water and swell, which makes them tighten onto the cornea, blur, and sometimes stick.
The options, in order of preference:
- Prescription swimming goggles. The clean answer. No lens, no exposure.
- Swim without correction if your prescription allows it.
- Watertight goggles over daily disposables, then bin the lenses immediately on getting out. Never reuse them, never put them back in a case.
Option three is a compromise, not a safe practice. If goggles leak — and they do — you have had the exposure.
For sport generally, see contact lenses for sports.
Showering
This one surprises people, because it feels like nothing. But shower water is tap water, shower heads harbour biofilm, and the spray goes directly into your eyes.
Take your lenses out before you shower where you reasonably can. If that is impractical, keep your eyes closed under the spray and keep your face out of the direct stream.
The same logic covers hot tubs, which are worse still: warm water is better growing conditions, and chlorine degrades quickly at those temperatures.
Tap water in the lens routine
Three habits to eliminate completely:
- Rinsing lenses with tap water. Ever, for any reason.
- Rinsing the case with tap water. This is the one people keep doing after they have stopped rinsing lenses — and the case is where biofilm forms. Rinse with solution, then air-dry face down. See the case guide.
- Topping up with water when solution runs low. No solution means take the lenses out; see solutions explained.
Wet hands are fine as long as they are dried on a clean, lint-free towel before you touch a lens.
Scleral lenses are the exception that proves the rule
Scleral lenses are filled with fluid before insertion — and that fluid must be preservative-free sterile saline, never tap water, never distilled water, never homemade saline. It sits against the cornea for the entire day, so the sterility requirement is stricter here than anywhere else in lens wear.
If you have already been exposed
Do not panic. Most exposures cause nothing. But do these things:
- Remove the lenses as soon as you can and discard them if they are disposable
- Do not put them back in that day
- Use fresh solution and a clean case if they are reusable, or better, start a new pair
- Watch for symptoms over the next two weeks
Seek care the same day if you get pain out of proportion to how the eye looks, light sensitivity, blurred vision, persistent redness or a feeling that something is in the eye that does not settle. See red eye with contacts.
And say the words out loud at the appointment: “I swam in my contacts,” or “I rinsed them in tap water.” That sentence changes what the clinician looks for, and early treatment is the single biggest factor in how these cases end.
Sources
- CDC — Acanthamoeba keratitis risk factors and prevention
- FDA — contact lens care and water exposure guidance
General information, not a substitute for clinical care. If your eye is painful or your vision has changed, be seen the same day. Reviewed by Dr. Teresita Bollar, OD.
