Depending on your filtration needs, specific particles can be targeted and removed based on size, down to the molecular level. This is accomplished through the use of membranes, semi-permeable barriers that filter out unwanted particles when water is passed through or across its pores.. According to the pore size of the membrane, there are 4 types, micro/ultra/nano filtration and reverse osmosis. All these technologies work under pressure, which drives the water onto the membranes. The sealing of the pores is provided with periodic rinsing, cleaning.