According to the CDC, more than 21 percent of American adults are not aware that swimming while ill with diarrhea can heavily contaminate pool water with Cryptosporidium (Crypto), a protozoan parasite that will make other swimmers sick. And while showering prior to entering a pool or spa is always a good idea, how many of us routinely enter a pool without doing so?

There are many microbial contaminants that enter pool and spa waters by fecal contamination. They include:

• Coliform Bacteria. These are a very large group of bacterial species. Included in their ranks is E. Coli, which causes severe gastrointestinal illness and kidney failure if the water is ingested. This kind of bacteria doesn’t usually proliferate in pool water, so its presence is an indication of fecal contamination.

• Protozoan Parasites. Giardia and Cryptosporidium are members of this family. They are more resistant to chlorine than a lot of other microbes.

• Norovirus. This is a highly contagious group of viruses that causes acute gastrointestinal illness.

Other microbes that can exist in swimming pools and spas include Legionella, which can cause Legionnaire’s Disease and is potentially fatal.

Pseudomonas is another class of bacteria that cause hot tub rash. It also causes swimmer’s ear.

In 2018, the Association of Pool and Spa Professionals (APSP) republished the American National Standard for Water Quality in Public Pools and Spas. This useful document gives all sorts of recommendations for chemical levels in commercial swimming pools.

Interestingly, the document does not recommend bacteriological or microbial testing. Other agencies such as the World Health Organization, the United Kingdom Health Protection Agency, as well as the South Australia Environmental and Public Health Service, have established testing standards for routine monitoring of public pools and hot tubs for microbial parameters.

According to the APSP, however, these sorts of tests are redundant and offer information about the microbial history of a pool rather than its current state.

The redundancy, they argue, lies in the fact that the EPA has already registered any agent that claims to be a sanitizer if it meets the following criteria: The standard heterotrophic plate count must not exceed 200 CFU/ml; and the total coliforms and fecal coliforms must not exceed 1 CFU/ 50 ml. (A heterotrophic plate count indicates bacteria that are capable of forming visible colonies under specified conditions. A CFU is a colony forming unit).

Thus, if properly used, sanitizers that meet these criteria have already established their ability to control bacteria under real world application.

In addition, the APSP also states that microbial testing only gives information about a pool’s history rather than its current state. Because testing usually requires 48 hours to obtain test results, any information obtained about the water quality is information that is two days old, and not information about the current state of the pool.

Further, they argue that monitoring for bacteria is not effective because a single test often gives false results; rather, hundreds of samples are required over an extended time period to obtain the desired information.

That said, there are many government agencies that do recommend microbial testing.

The United Kingdom not only recommends microbial testing, but requires it. They have the following requirements:

• Heterotrophic plate count less than 100 CFU per 1 ml sample.

• E. Coli test less than 1 CFU per 100 ml sample.

• Pseudomonas test less than 1 CFU per 100 ml.

Further, they require that these tests be conducted twice a month for commercial pools by an approved laboratory.

Currently, there are multiple commercially available kits for microbial testing available from multiple manufacturers. These tests usually come in easy-to-use test strips and can detect all sorts of bacteria and microbes such as Pseudomonas, E. coli, Salmonella, and many other Coliform and non-Coliform bacteria. Most of these tests can confirm bacteria levels of approximately 1000 CFU/ml. Some of these tests are quick as well, taking only 20 minutes.

The EPA has set the criteria for E. coli at a limit of 126 CFU per 100 ml in recreational water as the maximum safe level.

Therefore, maximum microbial levels still require laboratories for acceptable testing, a process that, unfortunately, takes time.

Table from 2018, the Association of Pool and Spa Professionals (APSP) re-published the American National Standard for Water Quality in Public Pools and Spas.