SWA does not have bottled water; it is actually canned (yes, odd I know.) It is provided via the beverage service, so you should get it halfway through the flight. The taste is a little off, kind of metallic.
If you are flying in the next couple of days be prepared for the possibility that all the water will all be gone by the time you get on the plane. People are waiting for several hours without access to water in some airports. A blog entry posted this morning by NBC producer Clare Duffy contained the following statement: "On board the plane now, a member of the flight crew is relating how even they were forced to throw away their lunches. There's no water on board, and we weren't allowed to bring any on board. This should be a fun six hours." The flight she was on was from JFK to LAX, she didn't say what airline, but with that route it was not SWA.
My personal guess is that in a few days the rule will be relaxed to say that you will be able to bring beverages on board if they are either 1) tasted in front of the TSO and airline staff as you enter the jetway, or 2) are still factory-sealed when you board.