Acanthamoeba Keratitis: This is the most likely diagnosis due to the exposure to contaminated water while wearing contact lenses. Acanthamoeba keratitis is a serious infection of the cornea caused by a parasite that can be found in water. It is known for causing painful blurred vision, redness, and sensitivity to light, especially in contact lens wearers who have been exposed to contaminated water.

Bacterial Keratitis: Bacterial infections can also occur after exposure to contaminated water, leading to painful blurred vision. The risk is increased in contact lens wearers, especially if proper hygiene practices are not followed.
Fungal Keratitis: Similar to bacterial keratitis, fungal infections can result from contaminated water exposure, causing painful vision and blurred vision.
Chemical Keratitis: Exposure to chemicals in the pool water, such as high levels of chlorine, can cause irritation and damage to the cornea, leading to painful blurred vision.

Pseudomonas Aeruginosa Infection: This is a serious bacterial infection that can rapidly progress and cause severe damage to the cornea. It is crucial to diagnose and treat promptly to prevent vision loss.
Herpes Simplex Keratitis: Although less directly related to pool water exposure, any condition causing corneal inflammation or damage can potentially reactivate herpes simplex virus, leading to herpetic keratitis, which is a medical emergency.

Naegleria Fowleri Infection: While extremely rare, Naegleria fowleri, the "brain-eating amoeba," can infect individuals through contaminated water, potentially leading to severe and life-threatening conditions. However, it primarily causes primary amebic meningoencephalitis rather than ocular symptoms.
Other Parasitic Infections: Other parasitic infections, such as those caused by Giardia or Cryptosporidium, are less commonly associated with ocular symptoms but could potentially cause eye infections in rare cases.