h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I feel I should point out that Vikor Sch.'s point of view is not exactly widely held amongst scientists. While it is true to say that exposure to microorganisms strengthens the immune system. That is not the same as saying that the microorganisms themselves strengthen the immune system, its just that we get better at fighting them off. Generally disinfection is only used for water from river and lakes (surface water) where there is a significant risk of contamination with harmful organisms. For anybody who wants to give their immune system a work out by drinking contaminated water they always have the option to go to their local river and drink a glass or two, but my experiences as a kayaker (which often involves involuntary drinking of water) suggest that the sickness this produces outweighs any benefits in terms of a better immune system (you never get completely resistent).

Essentially the point is, if you are going to give unconventional theories give the accepted ones too, because often the accepted ones are right.