you need a booster pump mate if you want to up production.
most good wfp suppliers sell them.
Just make sure you get the right one that suits your system.
I have 40/40 r/o and boosted it produces approx 250-300ltrs per hour.
I push this into holding tanks (IBC'S) then I run a couple of vans
.
If you only need 500-600 litres per day make it and store it
in IBC then use transfer pump to fill your van tank.
Russ