Originally Posted By: nursemike
My science is old and rusty: as I understand it, reverse osmosis means using pressure to force water molecules through really small holes/semi-permeable membrane against the normal flow of lower concentration to higher concentration. Does that men that pump water filters like the mini-works, or gravity filters like the Sawyer are committing reverse osmosis?

they're not reverse osmosis , if they were that fact would be heavily advertised,
A "manual reverse osmosis desalinator (MROD)," costs from one to two thousand dollars (katadyn)
Also
Originally Posted By: https://en.wikipedia.org/wiki/Reverse_osmosis
reverse osmosis requires that a high pressure be exerted on the high concentration side of the membrane, usually 2–17 bar (30–250 psi) for fresh and brackish water, and 40–82 bar (600–1200 psi) for seawater, which has around 27 bar (390 psi) natural osmotic pressure that must be overcome.


They're microfilters

Originally Posted By: http://www.cawst.org/es/resources/pubs/category/15-intro-to-hwts
Code:
Filtration Type      | Pore Size (µm / nm)    | Molecular Weight (Daltons)
Microfiltration (MF) | 0.1-10 µm (1-1000 nm)  | 
Ultrafiltration (UF) | 0.01-0.1 µm (1-100 nm) | 10,000- 500,000
Nanofiltration (NF)  | <0.001 µm (<1 nm)      | 200-1,000
Reverse osmosis (RO) | <0.001 µm (<1 nm)      | <100

Originally Posted By: http://www.princeton.edu/~oa/manual/water.shtml

Organism |Examples |General Size |Filter Type |Particle Size Rating
Protozoa |Giardia, Cryptosporidium |5 microns or larger |Water filter |1.0–4.0 microns
Bacteria |Cholera, E. coli, Salmonella |0.2–0.5 microns |Microfilter |0.2–1.0 microns
Viruses |Hepatitis A, rotavirus, Norwalk virus |0.004 microns |Water purifier |to 0.004 microns