What happens when water and bleach are mixed together?

Bleach is, er, *searches the back of his brain* Sodium Hypochlorite solution.

That means that it starts as the dry ingredient NaClO, and when you add water, it dissolves in it into Na+ ions, and ClO- ions, just like table salt will dissolve into Na+ and Cl- ions.

So, what happens when you add water to salty water? It gets more dilute. What happens when you add water to bleach? It gets more dilute. It's still bleach, it's just not as strong.