We are near the Pacific coast and a large public aquarium affiliated with a large university. So, we first tried to pick-up saltwater pumped from the ocean and sand filtered by the public aquarium and made available to local hobbyists and the university researchers. The water was free but we still had a two-way drive of almost an hour and water is heavy.
We strapped a 30-gallon drum into the back seat of an SUV. Probably not safe.
Why NSW? Mother nature must be better than artificial, so we thought. Some good things in ocean saltwater and also the risk of some bad things.
Next, we tried to purchase NSW from a commercial delivery service that advertised they got their water from the public aquarium system. These folks are usually aquarium maintenance companies that need saltwater on hand to service their clients.
Then we tried to buy natural seawater (NSW) from local fish stores (LFS) that in turn bought from commercial services pumping directly from the ocean.
Then, we tried to buy artificial saltwater made-up by the local fish stores.
Finally we tried to make-up our own using freshwater and a commercial salt mix formulated for reef tanks. So far, this is our preferred method.
For freshwater, we use a home RODI system. You can buy RODI water also, often from an LFS.
Note that we split our RODI system and use RO for drinking and cooking.