As previously stated, the coliform organism, because of the large numbers present in fecal matter, offers a far more satisfactory approach to the detection of the presence of fecal contamination than would a search for the pathogenic organisms. Since the incidence of pathogens is related to the presence of infected persons in the community, there may be long period of time when fecal contamination is present, but specific pathogens would be absent. Thus, a search for a specific pathogenic organism might be fruitless. Moreover, throughout the time required to make the necessary examinations, people would continue to consume the water. This delay in determining the hazardous nature of water could easily result in a waterborne-diseases outbreak. Furthermore, Test procedure would have to be definitive for all of the organisms causing the various waterborne diseases. Such a procedure is not presently available, nor is it likely to be developed in the near future. Although the waterworks profession relies on the coliform examination to determine whether water is free from disease-producing microorganisms, this test for water safety does have its limitation. What is the response of other biological organisms to various treatment processes? Can it be assumed that the treatment reduces all pathogenic organisms to the same extent that it reduces coliform bacteria?

Accumulated evidence indicates that the bacteria causing typhoid, paratyphoid, cholera, and bacillary dysentery respond to treatment in the same manner as coliform bacteria. Some viruses, however, appear to persist in water for longer times than coliform. Viruses may penetrate through rapid-sand filters more readily than coliform bacteria. Certain viruses are known to be more resistant than coliform to destruction by chlorine disinfections. From these observations, one can only conclude that it is possible for certain pathogenic organisms to survive treatment that apparently removes or destroy all coliform bacteria.

Despite this possibility the record of waterborne-diseases outbreaks attributable to properly treated public water supplies indicates that the coliform bacterial examination has served as a satisfactory measure of the man's natural immunities, the low incidence of waterborne diseases in the population, and the fact that many raw waters, particularly the more polluted ones, are treated by processes providing good clarification and heavy chlorination. With good clarification and exposure to substantial levels of free chlorine residual over extended periods of time, there is an excellent chance of removing or destroying any virus that may be present in the raw water.Considerable research is being done in the area of water bacteriology. Fecal streptococcus is being studied, cultured, and compared to fecal coliform. Virus culturing techniques are being studied and improved. Gastroenteritis is being studied to better define the causative agents as well as its control. Through such efforts, microbiological pollution control will keep pace with future developments.