While looking for a solution to solve a problem I am having with my fresh water fish tank, I came across a tap water filter.
A deionizer to be exact. From my understanding, deionized water is ever better than RO water. Anyone that is a expert in water (Jimscott?) please comment on this as I would be very curious. It says in the FAQ that some people run RO water through this thing to make the RO water super pure, but doing so also saves the Deionized cartridge... But I don't think you can beat it for 29.69 for the device, and refill cartridges for 16.19 for one 43.19 for 3 and 80.99 for 6.
deionized tap water filter
EDIT: (added just for you Cassie) The prices given here are LIMITED TIME ONLY!! SO GET YOURS NOW! 10% OFF NORMAL PRICING FROM THE SITE GIVEN!