|MadSci Network: Microbiology|
I would not suggest that your relatives continue this practice and here is why.
E. coli is a gram negative organism, which means that it has a slime layer protective coating around it. This layer makes E. coli difficult to kill, and it does well with oxygen unlike other stomach organisms that must have anaerobic conditions.
The problem with E. coli is that as long as there is a source of food, which is plentiful in the top soil (carbon sources), and water it will stay alive. Many E. coli outbreaks have occured in the U.S. from water seeping through the cow pastures and into ground water sources. This ground water then is drawn into homes through wells.
I would guess that the sludge from your relatives septic tank is also seeping into the ground water.
There are certain treatments that can kill all bacteria in a septic tank; however, this defeats the purpose of having the tank in the first place! It is better to just get it pumped out on a regular basis. Planning ahead would be key. Another alternative would be the installation of a bigger tank or sometimes additional small tanks can be added to current systems.
Best of luck!
Try the links in the MadSci Library for more information on Microbiology.