I think the price of RO
varies from area to area. Where I live some places sell RO
for about 0.30/gal
while other places sell it for 0.50,if you have a selection of LFS
around town you may want to call around, since if you are buying water that size tank it $$$ will add up quickly (considering you have a new tank you will have to change your water more frequently). You may want to invest in a RO
unit, it may cost you a lot up front, but will save you money in the long run.
As for what RO
stands for Reverse Osmosis and Deionization. If you want to find out what it is just do a search on the topic. This one is from the articles section.
How Reverse Osmosis Systems Work