Same as my situation, though i started with a 75GPD ROI have added a second membrane to push up to 150GPD. I have a 100psi shurflo pump which im going to hook up to my RO when i get chance. When adding a booster pump to the RO, make sure the pump goes just before the membrane. A mistake i made.This is how the system should go Tap - pre filters - pump - membrane - di filterA 4040 would be better as production is quicker. Depends on the funds avalible though. If your interested in a 4040, then GAPS water is your place. They do special 4040's for those with low pressure.Any other questions feel free to email me. JP