Why are chlorine compounds safe?

Chlorine
Chlorine is highly reactive and it is moderately dangerous in many forms. That is why it is so useful. In your example, chlorine is used in municipal water systems to KILL THINGS. Same in swimming pools. If you are using Chlorox at home, you should use gloves since it will damage your skin even at the low concentrations you buy in stores. (You usually dilute it significantly for cleaning.) That said, it comes down to concentration and protection. You can put chlorine compounds in drinking water and swimming pools because the concentrations that are lethal to bacteria don't significantly hurt people. Our skin is sufficient protection. The reason chlorine gas is so dangerous is that you don't have any protection against it. When you breath in Cl2, it goes right into your vunerable lungs, reacts with the moisture there and becomes HCL. Having a strong, reactive acid in your lungs is not good.

Touched on in the previous: reactivity!

Chlorine in the diatomic gas form is highly reactive.

On the flip side, chlorine in the solid crystal NaCl is soluble in water, but basically non-reactive. Good thing, too, since NaCl is table salt.

Sodium (Na) is the same. Metallic sodium is incredibly reactive...mix with water and you get this wonderful hissing flame, giving off hydrogen and forming NaOH (also nasty stuff: sodium hydroxide is a powerful base/alkali).

Thank you both, but it was too late. Nonetheless I got the right answer.

Should have asked sooner.