Rinse with plain water immediately. That's it.

Yes, just run it under cold tap water as soon as you’re done swimming. Salt crystals are what cause damage—they dry into sharp little bastards that cut fibers. A thorough rinse gets rid of them.

You don’t need special detergent, vinegar, or any tricks. Salt water is pretty gentle on swimsuit fabric compared to chlorine. The real killer is letting it dry without rinsing. Then the salt concentrates, fades colors, and makes the elastic brittle. So rinse within a few hours.

Don’t wring it out or toss it in the washing machine on a regular cycle. Hand-wash gently with a bit of mild soap if you must, but plain water does the job. Hang to dry out of direct sun.

Future you will appreciate not having a saggy, stretched-out suit.