In order to filter out particles, salts, molecules, organisms smaller then 1 µm, you need techniques based on membrane filtration. Usually you need higher pressure, except for forward osmosis.
Membrane Filtration such as
Antiscalants
Cleaners
Food & Dairy Membrane Filtration (MF-UF-NF)
Forward Osmosis Membranes
Membranes For Membrane-Bioreactor (MBR)
Micro filtration membranes
Nano filtration membranes
RO-Membranes (brakisch and sea water; low energy, low fouling or high rejection types)
Ultrafiltration membranes (inside-out or outside-in)