What should i buy to purify my water?

[Zoaelite]

SP it was a weird comparison but think of the concept behind it. For a reef tank that has $1000's of dollars invested in livestock you wouldn't want to cheap out and put something that could potentially kill that live stock. Same with a BMW or any luxury car, use of a higher end fuel reduces the chance of damage/ wear and tare on the unit. You do have a good point, people should be measuring there TDS before deciding what RO to purchase. In the end though a RO also removes chlorine and other impurities in the water that could be entering your system.
I would never put tap water in my tank, as it just spells hair algae for me :\.