Long story short... I am looking at buying another tank to store in my garage facility to make pure water. I'm currently making it straight into my transit which is becoming an ever increasing pain as I'm having to move my booster pump outside everytime I need to re-fill my tank. I wan't a nice little set-up in my garage composing of a Merlin RO System (currently in my van also), Booster Pump, 650 litre Tank and a D.I. Vessel. Then I will be able to work in the day while producing it at the same time. I can then bilge pump it straight to my van after my shift in 10-15 minutes. But my question is: My current D.I. Vessel in my van is 11 Litre. This takes up nearly a whole bag of Tulsion a time (£70). Would it be more cost efficient to buy a smaller D.I., for example, 4.6 litre vessel to produce my pure water? Has anyone done the maths to work out how much pure water you can produce with an 11L vessel and a 4.6L Vessel, before changing the vessels? Basically how much pure water can you make with both sized vessels before changing the vessels resin thus trying to save money. Hope that makes sense, I tried. James.