UF is the abbreviation for ultra-filtration membrane, which is a similar membrane to RO membranes but with bigger pores which cannot remove dissolved salts from water. The big advantage of UF water purifiers is that it will work with or without electricity and completely remove all microorganisms from water including the smallest of viruses. Ultra filtration membrane water purifiers are as good as Reverse Osmosis water purifiers when used with public or Municipal supplied pipe or tap water. Piped tap water will not have problems with dissolved salts of toxic chemicals like Arsenic or Heavy Metals. RO is only required when the water has too much dissolved salts