It is not as complicated as shown. Water treatment is straightforward. Anyone can build a reverse osmosis water filter. Below: the basic principle of an RO system:

Before RO, water passes pre-filters to remove sediment, sand, rust and particles – extending membrane life and improving efficiency.

The semipermeable membrane is the heart: water molecules pass; larger contaminants and dissolved solids are rejected. Pore size typically 0.0001–0.001 µm.

RO is slow; a tank stores permeate for quick draw-off. Tankless systems (DirectFlow) need larger membranes, more pressure and often pumps and electronics – tanks remain popular for simplicity.

RO water can taste “flat”. Activated carbon post-filters refresh taste; further mineral or media stages are widely possible.