The survival of seven F+RNA phages (MS2 Group I ATCC type strain, two Group I environmental isolates, a Group II environmental isolate, a Group III environmental isolate, and two Group IV environmental isolates) and six F+DNA phages (M13, fd, f1, and ZJ/2 ATCC type strains, and two environmental isolates) were examined in microcosms using a surface drinking water source. Phages were spiked into replicate aliquots of a source water at about 20,000 pfu/ml. Replicate spikes were incubated at 4 and 20°C and monitored for 110 days. At 4°C, Groups I and II F+ RNA phages were detectable through 110 days, with reductions of about 1 and 3 log10, respectively. The Group III F+RNA phage demonstrated 5 log10 reduction after 3 weeks, and the Group IV F+RNA phages were reduced to detection limits (5 log10 reduction) within 10 days. Of the F+DNA phages, all four type strains were detectable with about 2.5 log10 reduction after 110 days at 4°C. The F+DNA environmental isolates were detectable with about a 4 log10 reduction after 110 days at 4°C. All phages demonstrated faster decay at 20°C. These results suggest that differences in F+ phage survival may influence their prevalence in environmental waters and the ability to attribute their prevalence to specific human and animal sources of faecal contamination.