I know you are looking for it to be an accident...so if you are going with this method in your swimming pool...then this is all I have as far as an idea.
Since everyone knows you cannot swim...sign up for swim class (bare with me) take a couple, then do what great-ape99 said, wear yourself out, then jump in the deep end. With any luck it will work because you will be so exhausted and shaky and people will think you drowned trying to practice alone. Again....you would have to sign up for swim classes and show up at least 2x so that people will believe it when they find you.
(or hope that they would)