What culture medium should we use for tap/drinking water bacteria?

Question

We are a group of high school students from Manila who is performing an investigatory project on a topic that we chose which, at first glance, seemed simple, but turned out a bit complicated. We're trying to test the effectiveness of SODIS of solar water disinfection in killing bacteria.

I previously asked a question here at Stack Exchange and we consulted our teacher about the answer we received. According to her, at our level, it is best to use culture media. Our testing will be qualitative. We won't be identifying the specific type of bacteria. Rather, we will observe culture media if anything grows in there.

She gave us an assignment to research about what medium to use. Due to inexperience and lack of knowledge on what we find on the internet, we resorted to ask here again.

For bacteria commonly found in tap water, what culture medium do we use? We found mentions of Legionella, Salmonella, E. coli, and Anabaena sp. in our research.

In this article, we found different types of culture media. TSA captured our attention because it is a "general type." Nonetheless, we're not that sure about what "general" means if it means it can be used for the bacteria I mentioned above. There's also EMB that appears to be used in two of the bacteria we mentioned.

Edit: It appears that not all culture media is good for student use. According to this article, only LB Agar, Nutrient Agar, and Tryptic Soy Agar can be used by students. Among these three, is there something I can use?

Answer 1

Usually when culture-based methods are used to test drinking water a range of selective culture media are used (media that favor the growth of a specific category of bacteria, e.g. the MacConkey Agar mentioned in the article you linked to). This is because the aim is to test for the presence of known harmful bacteria.

I would suggest that any of your suggestions (LB agar, Nutrient Agar or Tryptic Soy Agar) would work just fine.

On another note: How are you inoculating the agar? The concentration of bacterial cells in tap water is very low, to test for bacteria usually a large volume (~ 1 liter) is passed through sterile filter paper which is then pressed onto an agar plate to transfer the bacteria.

Answer 2

As an adjunct to your research, i would advise that you visit your local water authority to gain more insight into the process of testing water for bacterial contaminants using culture media. They will usually point you to a commercial lab that does the testing for the local water authority. That commercial lab will provide you a wealth of information, especially on why a particular medium or media is used to test local water samples.

Another source of information may be your local hospital. Visit their clinical lab and query if they have conducted water tests using culture media. They too will provide a wealth of information.