In or near real-time monitoring of fluids can take place using an opticoanalytical device that is configured for monitoring the fluid. Fluids can be monitored prior to or during their introduction into a subterranean formation using the opticoanalytical devices. Produced fluids from a subterranean formation can be monitored in a like manner. Specifically, bacteria can be monitored in fluids using opticoanalytical devices. The methods can comprise exposing water to a bactericidal treatment, and after exposing the water to the bactericidal treatment, monitoring live bacteria in the water using an opticoanalyfical device that is in optical communication with the water. Optionally, the water can be introduced into a subterranean formation.