A method for monitoring bulk (total) microbiological water activity and surface associated microbiological activity in a process stream comprising: a. connecting an apparatus to a process stream, wherein said apparatus comprises a flow cell containing a plurality of openings, wherein at least one opening is a flow cell inlet for fluid drawn from said process stream and at least one opening is a flow cell outlet for fluid exiting said flow cell; a DO probe containing a DO sensor head, wherein said DO probe is attached to one of said openings and wherein at least a portion of said DO sensor head protrudes into said flow cell; an ORP probe containing an ORP sensor head, wherein said ORP probe is attached to one of said openings and wherein at least a portion of said ORP sensor head protrudes into said flow cell; a cleaning device attached to the flow cell; a first conduit attached to the flow cell inlet; a second conduit attached to the flow cell outlet; and a valve that is attached to said first conduit, wherein the apparatus is connected to the process stream via said first conduit; b. opening the valve of said apparatus to allow fluid to be drawn into said flow cell; c. drawing fluid from said process stream into said flow cell; d. measuring at least once the DO concentration of said process stream with said DO probe, and wherein prior to each measurement the surface of said DO probe is not cleaned; e. cleaning the surface of said DO probe; % f. measuring at least once the DO concentration of the fluid inside said apparatus with said DO probe wherein prior to each measurement said DO probe surface is cleaned; g. closing the valve of said apparatus to prevent fluid from being drawn into said flow cell; h. measuring at least once the DO concentration of the fluid inside said apparatus with said DO probe, and wherein prior to each measurement the surface of said DO probe is cleaned; i. calculating a Δ DO reading between step (f) and step (h) and correlating said Δ DO value with bulk microbiological activity in said process stream; j. calculating a Δ DO reading between step (d) and step (f) and correlating said Δ DO value with surface associated microbiological activity in said process stream. a. connecting an apparatus to a process stream, wherein said apparatus comprises a flow cell containing a plurality of openings, wherein at least one opening is a flow cell inlet for fluid drawn from said process stream and at least one opening is a flow cell outlet for fluid exiting said flow cell; a DO probe containing a DO sensor head, wherein said DO probe is attached to one of said openings and wherein at least a portion of said DO sensor head protrudes into said flow cell; an ORP probe containing an ORP sensor head, wherein said ORP probe is attached to one of said openings and wherein at least a portion of said ORP sensor head protrudes into said flow cell; a cleaning device attached to the flow cell; a first conduit attached to the flow cell inlet; a second conduit attached to the flow cell outlet; and a valve that is attached to said first conduit, wherein the apparatus is connected to the process stream via said first conduit; b. opening the valve of said apparatus to allow fluid to be drawn into said flow cell; c. drawing fluid from said process stream into said flow cell; d. measuring at least once the DO concentration of said process stream with said DO probe, and wherein prior to each measurement the surface of said DO probe is not cleaned; e. cleaning the surface of said DO probe; % f. measuring at least once the DO concentration of the fluid inside said apparatus with said DO probe wherein prior to each measurement said DO probe surface is cleaned; g. closing the valve of said apparatus to prevent fluid from being drawn into said flow cell; h. measuring at least once the DO concentration of the fluid inside said apparatus with said DO probe, and wherein prior to each measurement the surface of said DO probe is cleaned; i. calculating a Δ DO reading between step (f) and step (h) and correlating said Δ DO value with bulk microbiological activity in said process stream; j. calculating a Δ DO reading between step (d) and step (f) and correlating said Δ DO value with surface associated microbiological activity in said process stream.