Mine is 8 Stages, on its first phase.
It's not an original products. Basically, I just buy random products and DIY it.
1, Descaler (Treat Tap Water)
2, PP Carton (Dirt remover at 1 micron)
3, Dirt Membrane (Dirt remover at 0.1um)
3, GAC (Carbon Pre-filter)
4, Carbon Block (Carbon Post-filter)
5, Carbon Block (Carbon Post-filter)
6, RO Membrane 600gpd
7, DI Resin (Recycle System)
8, DI Resin (One-time throw away)
Then it would be 0 TDS and saved in Plastic Reservoir with circulating pump 24/7 and now added a UV system to it.
Then it would go through another 3 stage of DI Recirculating System when releasing into mixer reservoir, although this last 3 stage is not needed, I think. But since I have it, so I just let its work.
But I think it's the UV, that kills whatever filter couldn't removed.