pumping water through RO/DI?

[MarkoD]

so what im trying to do is pump water from a barrel into my RO/DI instead of having it come from the house pluming..... this way i can put the waste water from the RO/DI back into the barrel and get 100% efficiency.

I tried hooking this up with a 1900GPH pump and it wasnt enough pressure to push through.... i get water coming out of the waste line but no good water.

any idea how big of a pump i'd need to get this going?