JD, someone else will have to chime in as to the legality in your area.
As for the first question, there are a lot of strong held views here iether way, by folk with far more experience than me, so you will have to see what the others say and make your mind up.
It is very common out here to use fresh sea water if you live close to the coast. I do for two reasons, cost and practicality... my PWCs are between 100 and 150 Ga and I couldnt be bothered with the mission of mixing up salt and RO to accomplish that when I have a perfectly good free alternative. That said, there are some riders that go with this....
Our ambient and water temperature is very close to my tank temp so the water does not need to stand and acclimatise for too long with a possible die-off of plankton etc.
I only pump water on a clean day, far away from sewerage, industrial and rainfall/ river outfalls and out of fairly deep calm water.
I test water parameters (now- on advice from here)
Water being pumped into my tank gets filtered through a fine mesh to prevent a reoccurance of two previous problems... a mantis shrimp got into my system via a pwc and later- just to prove that you never learn from mistakes
- a cracker shrimp got in the same way (Both in my previous system) The mantis is an obvious pest, the cracker has an ominous side, they make a sound with their tails as loud as a gunshot and can crack 1/2 inch tank glass... both are almost impossible to remove without breaking down your tank.
In short, it depends on your circumstances and you need to be aware of the potential for introducing both hitchhikers and pollutants into your system. There are some other intelligent and well thought out arguments against the practice from smarter people than me here so either search the site for previous discussions on the topic or wait for someone to chime in with the argument against before you make up your mind.
