I have a RO man system and they have a pressure regulating booster pump for £60 + vat. Matbe worth a look. Not sure how that would wire up? Had a look at the diagram, straight over my head... 
checked my TDS out of Ro and it was 001 and thats with crap pressure. Do I really need to run it through the DI vessel?
Just been on the phone to ro-man, i think the pump you are on about is the domestic pump which they said is only able to be used for a hour per day as it will burn out and only really boost your water output to around 40 litres a day. They have said for window cleaning purposes you will need the heavy duty pump which costs around 200 quid

and will boost the pressure to 80psi which is whats needed for powering the whole upgrade to get the amount of water required.
I bought the upgrade to give me more water but found with going through the extra membrane its giving me less because ive got crap water pressure, now im back to square one dont want to pay 200 quid for a pump.

Im thinking about getting 2 of those blue vessels as i have a large bag of resin, could i do it this way from my outside tap if i need a large amount of water without a pump? Just for emergancies only , am i making sense

any advice please

Brett