One thing that you can try to do, is to use sun screen with a mixture of water. You could choose to just use a water based sun screen in the first place, instead of having to mix it with anything. Now take this sunscreen and apply it to the suit. This will help protect the suit from the rays of the sun.
The sun can sometimes end up causing suits to get yellow marks on them, which is why this is a very cheap and easy way to make sure that it ends up staying white and fresh.
The next best thing for you to do, is to go on and wash your swim suit right after you use it. Now this needs to be done in a specific manner. Firstly, don’t wash it with any coloured clothes or swim suits, since the colours could end up leaking and ruining the suit altogether.
Instead, look to run it under cold water on its own right after you use it, this will end up cleaning it up of any impurities that it might have picked up. After you do so, you can go on and wash as you would a normal suit, but separately.
The last thing you can do, to make sure your white suit doesn’t end up getting ruined, is to never really swim in it. Now this might sound like an odd thing to do, but this is the smartest possible way to keep it from getting ruined.
Not using it will ensure that it never gets dirty, and that it never gets any stains, so if you want to keep it in top shape, then not using it is the answer.