I built my own 3 stages DI water system! For some reasons, our water has low TDS (around 50) but has some discoloration so I do Sendiment-Carbon-DI. I retrofit the CR Spotless cart since I use the system to clean the House Windows and Solar Panels couple times a year.
I just use the Shutoff valves and T for bypass. The stainless steel hose appeared not to affect the flow! Also add a flow metter to monitor flow and total consumption.
I spent less than half the price of the CR Spotless.
You could tell the water before and after
One of the best things I purchased. Now I could wash the car anytime and don't have wait for the sun to go down and dont even blow/wipe the cars after unless I apply sacrificial detailer afterwards.