So here is my pondering....... My TDS from the tap is 150ppm not bad not super good neither but serves me well. I make about 3000 liters of pure per week through a 20" RO at about 10ppm and then finish with a 6 liter DI to reduce to 0 ppm. So in total about 9000 liters per week (Including waste). That's 36'000 liters per month, totaling 216,000 liters on average before my TDS starts to creep up and it's time for a resin change. Now IMO 144'000 liters of waste water per six months is rather excessive and not very environmentally sound so I am contemplating how to reduce this. Now obviously water produced through DI has no waste water so seems to me the more environmentally sound option. Now I am considering 2 x 25 liter DI vessels with carbon and sediment pre filters of course. Now currently my water per liter production cost is so low it's almost pathetic and if I switch to DI it will increase somewhat but the waste will be eliminated. As suggested in another thread I would probably fit this to the van, fill the tank with tap water so the production through the DI is nice and slow to extend the resin life and water quality. Does anyone currently run a similar setup, with similar TDS or have the scientific knowledge to figure out roughly how many liters I will get before needing to swap the resin out?