Do you have a TDS meter? If you do, you can use it to test the water and make sure it doesn't have too much nutrients in it. I read that RO water is lower in nutrients that tap water, but still can have a lot of the heavy metals that the DI system can take out. I think you can use it if you are using tap water now, but if you have any algae issues after it. You will always have the doubt about the water source you are using.
Buying an RODI unit is your best bet. It will be expensive, but it will pay for itself in the long run. I hope someone with more experience can answer your question better than me.
