Ultrafiltration (UF) is a variety of membrane filtration in which forces like pressure or concentration gradients lead to a separation through a semipermeable membrane. Suspended solids and solutes of high molecular weight are retained in the so-called retentate, while water and low molecular weight solutes pass through the membrane in the permeate. Wickipedia...
 
Basically, water in the system under pressure is forced through straws with holes in them followed by smaller straws with smaller holes and so on until the water is filtered down to .0135 microns or better depending on the membrane one is using. So basically, this technology filters 100 times better than a one micron filter.
Ultrafiltration does have its draw backs. It doesn’t purify (removing everything and leaving behind just water) the water like Distillation, Reverse Osmosis or de-ionization but, it filters so well that the user can eliminate the need for Ultra Violate technology for sterilization and the electricity required to power the UV lamp. Because it filters down to a size smaller than a virus, it allows post filters to be filters collecting contaminants that they were designed for and extending the life of the filter dramatically. It’s a win win!