After the first 48 hours post-application, your lashes will be completely waterproof. You can swim with them, shower, and wash your face. Just remember to avoid rubbing or pulling on your eyelashes, as this will increase their risk of falling out.
Some salons mist lashes with water at the end of every appointment since water helps cure lash extension adhesive. Ask your salon if their lasts are chlorine and salt waterproof. Even if they are, you should rinse your lashes after swimming to remove any salt residue.