Low pressure membranes are a widely used drinking water treatment technology to reject particles and microbiological contaminants. A commercial UF membrane was used to investigate the removal of two virus surrogates (MS2 and phi X174 bacteriophage) of similar size but with different surface characteristics. MS2 was better removed than (phi X174 regardless of its smaller size. phi X174 removal was found to decrease significantly as the feed solution pH increased from 6.5 to 9.4. Using mathematical modeling, size exclusion was confirmed to be the main removal mechanism for both bacteriophage. These values were then compared with experimental results and virus characteristics to evaluate the contribution of other removal mechanisms. The additional removal for MS2 above baseline size exclusion was likely a result of electrostatic repulsion. For phi X174, adsorption was shown to increase rejection at pH 6.5, but at pH 9.4 removal was due solely to size exclusion. The higher isolectric point of phi X174, along with its complex capsid structure, are believed to be responsible for the different removal patterns between the two phage types. (C) 2013 Elsevier B.V. All rights reserved.