Water Filters That Remove Total Coliform

One of the goals of the Safe Drinking Water Act is to establish standards for elimination of waterborne pathogens, which are disease-carrying organisms in water. The main test for organic purification is the total coliform test. In this test, the laboratory looks for the presence (above a certain level) of coliform bacteria. Filtration is one method of removing coliform bacteria from water. At roughly 0.50 microns, coliform bacteria are relatively large and easy to remove.

Microfiltration

• Filters are graded by the size of particles they will remove. Membrane filters are the most common used in water treatment and are formed from cellulose acetate or polyamide-composite. Microfilters are membrane filters removing particles as small as 0.01 microns (100 angstroms). A filter can be classified as a microfilter if it removes particles no smaller than 10 microns.
  Because most coliform bacteria are larger than 0.50 microns, higher grade (removes smaller particles) microfilters can remove total coliform. Read the size rating of the microfilter to be sure it will filter 0.1 micron or smaller particles. Do not assume all microfilters will remove total coliform.

Ultrafiltration and Nanofiltration

• Filters classified for ultrafiltration will fall in the range of removing particles from 0.1 down to 0.001 micron. Nanofiltration filters range from 0.01 down to under 0.001 micron. Either type of filter will remove total coliform.

Reverse Osmosis (RO) Filters

• The highest level of filtration commercially available is the reverse osmosis filter. Because of the small size of membrane openings, reverse osmosis filters require pressure to force a percentage of water through the filter. Reverse osmosis filters can filter down to the 0.0001 micron (1.0 angstrom) range. Any reverse osmosis filter will remove total coliform as well as other bacteria, virus, colloidal metals and most dissolved organics.