The latest designs of Doulton filter elements incorporate Oligodynamic silver impregnated into a porous ceramic outer shell [80,000,000 pores] that can trap bacteria down to as low as .22 of a micron in particle size [1/100,000 of an inch]. Laboratories consider a filtering medium with an effective pore size of .01 micron to .45 micron to be bacteriologically sterileand .45 micron to 1.0 micron to be bacteriologically safe.

Regrowth of bacteria that becomes trapped either on the outside of the element or in the ceramic's pores is controlled by the silver which, on contact with water, releases small quantities of positively charged metals ions. These ions are taken into the enzyme system of the bacteria's cell and thereby neutralize it.