seriously guys, he is right, tap water and table salt(i hear) is best for an aquarium. and if you cannot get table salt any salt substitue should be fine
NOT, do not use either in your tank, PLEASE. Tap water can work(at best, it can but not the best AND most of the time it can be detrimental), but 99.99999999999999999999999% of the time it has impurities of some type in ther that should not be in a sw tank, at all.
and just a disclaimer there, table salt would be a very bad idea. That is one that will NOT work, or even get by at all.