The very same thing has happened to me. I now try carefully never to step on the white tiles, even when its not raining. They are so dangerous. I have also seen other people fall on them when its raining. A death trap!
Yep, you have to watch out for those white lines. Not only when it is raining, but when the path cleaner machine has gone by. The surface must be 20 years old at this stage, no one had heard of Health and Safety back then! Still, it is not as dangerous as the path/road markings at the GPO, where I believe at least two people have lost their lives.