His-tag purified phage tail tip conjugated to a colorometric enzyme is added to a water sample by drawing water into a syringe. The tail tip recognizes LamB, an outer membrane protein on E. coli and binds to any E. coli present in the sample.

The solution is syringe filtered through a 0.45 micrometer filter to trap bacteria bound to phage tails and allow any unbound phage tail through. This prevents false positives by ridding the solution of excess phage tail for step three.