Most people assume the sole purpose of braces is to straighten teeth, but they actually serve a few other purposes. Braces may be used, for example, to correct an improperly aligned bite, which is the way your top and bottom teeth meet.
Braces and Water
Since braces consist of titanium alloy or other, similar materials, they are rust-proof. This helps both in the pool and, more generally, with saliva in the mouth. If braces were made of a material prone to rusting, pool water would likely make them rust, but so, too, would saliva. Based on this, there is no reason why you cannot go swimming with braces in your mouth.
If you are swimming laps or just lounging in the pool, you will not need to take any special considerations with your braces. If you are playing a sport where there is the possibility of body contact, however, you should be using a mouth guard to protect your braces. Playing water polo or water volleyball, for instance, would be two instances where you would want to protect your braces with a mouth guard.
Swimming With Retainers
After braces come off, many people begin wearing a retainer. Teeth will continue to move around, after all, and a retainer helps keep your teeth in the position your braces left them in. Unlike braces, orthodontists recommend that you take your retainer out before swimming and before any other vigorous physical activity. If you wear a retainer during vigorous physical activity, you risk having it slip out of your mouth.