I took my TDS meter to a few stores and couldn't believe the TDS was higher or the same as what was coming out of the tap. There is a water store in the north end near the Brick that may be a bit better but I don't think they change the cartridges often enough at the local grocery stores for the amount of water they go through. Its fine for drinking but IMO, not good enough for SW fish tanks.
There are a lot of used RODI units for sale right now, you'd just have to replace a few filters and you'd be good to go. I spent a lot of time fighting various algaes suffering along with water from the grocery store before breaking down and buying my own RODI unit. I really wish I'd done it sooner as my tank totally turned around and has paid for itself over and over in my less frustration and increased appreciation of my tank
