Both Escherichia coli and Enterococci were collected in foam within 7?min from 500 mL of bacteria-spiked water by coagulation and foam separation using ferric chloride and milk casein. These bacterial DNA isolated in the 100??L of extract from the foam more than 87.5% recovery using the DNeasy PowerWater? Kit. To test this method with water from three natural rivers, 0.67?2.70??g of DNA were concentrated in 100??L of extract from 1,000 mL of river water. When the DNA extract was subjected to 16S rRNA gene sequencing analysis, information on the bacterial flora could be obtained.