After a lot of feedback, I decided to post a walkaround of our DIY pure water cart. This is not a comprehensive howto, but hopefully with these closeups, and a little explanation, you'll be on your way to your own build. Parts we used below, not a comprehensive list, quantities will vary based on your needs. But this will get you started. And of course, your results may vary, so you assume your own responsibility.

The dolly was used, and craigslist or facebook are usually loaded with similar ones for cheap.

Prefilter
https://www.amazon.com/SimPureFilter...


Prefilter housing
https://www.amazon.com/EcoPureEPW2U...


RO pressure vessel
https://www.ebay.com/itm/ReverseOsmo...

RO membrane
https://www.ebay.com/itm/CWXLE4040...

DI filter housing
https://www.ebay.com/itm/233901314569

DI cartridge
https://www.amazon.com/gp/product/B01...

Inlet hose valve
https://www.amazon.com/gp/product/B08...

3/4 to 1/2"npt adapter
https://www.amazon.com/gp/product/B07...

3/4"npt to garden hose adapter
https://www.amazon.com/gp/product/B07...

Pex ball valve for flushing
https://www.amazon.com/gp/product/B08...

Pex tees
https://www.amazon.com/LTWFITTINGLea...

Pex elbows 90°
https://www.ebay.com/itm/10New12x...

Garden hose quick connect to wfp adapter
https://windowcleaner.com/xeropremiu...

Garden hose to quick connect with valve
https://windowcleaner.com/gilmouron...

1/2"npt to garden hose (probably don't need this one, but just in case)
https://www.amazon.com/GESHATENConne...

DI resin
honestly, window cleaning resource is the most economical choice, so hit them up!

Pex pipe
https://www.lowes.com/pd/SharkBite1...

Pex pipe clamps
https://www.amazon.com/LOKMANClamps...