Contaminants in drinking water vary in size considerably from grains of sand and grit that we can see to viruses and soluble salts that we cannot see. The contaminant or particle size determines the type of filtration required or able to remove it. For instance 1 micron filters are able to remove or stop particles greater than 1 micron such as sand, silt, algae and a large portion of bacteria.
Micro filtration or finer is required to remove particles greater than 1 micron along with some viruses and all bacteria. For greater contaminant removal, finer filtration such as Nano filters would be needed remove all of the previous contaminants plus some dissolved organics and salts. Where the maximum contaminant removal is required, Reverse osmosis would be used as this is the highest quality of filtration available. Micro, Nano and Reverse osmosis filtration all use membranes to achieve the required level of contaminant removal or reduction.
The micron rating in the chart below indicates the absolute micron rating of the filter required to remove the contaminants not the nominal rating. For further information on this please refer to the glossary of terms.