Do I have to have a rodi unit?

1. Is a Ro/Di unit all that necessary for a 50 gallon fowlr tank?
2. I have a filtered water in my kitchen next to the tap water, can I used that instead?
3. What are the furture problems that I'll most likely have if I used my filtered water (I will also dechlorinate it)?
4. If I have no other choice, can this rodi unit be portable ?http://ift.tt/1mhuSvB