551 Mr Liang. When we go swimming, the natural tears that bathe our eyes all the time are washed away, and so the eyes are irritated. Our eyes, in response to any substance that is an irritant, will turn red.
Pure water is an irritant as it is a hypotonic solution.
If the water contains substances or chemicals that are also irritants, the reaction is worsened. On the other hand, some substances, when added to water, can make the solution a non-irritant. For example, most eye drops are water based and yet they do not irritate the eye.