What is E.coli?
E.coli (Escherichia coli) is a bacteria, and is in the faecal coliform subgroup. It lives in the intestines of warm blooded mammals, including humans. While E.coli is healthy and naturally occurring, it can make us sick if we ingest it in our drinking waters, or are exposed to it while swimming or engaging in other recreational water activities. E.coli plays a central important role in measuring the health risks associated with sewage and contamination for natural water bodies, such as lakes, rivers, swimming holes, and marine beaches.
Why is E.coli important in recreational water monitoring?
E.coli is naturally occurring in our environment. E.coli is a reliable indicator of faecal contamination in our water bodies, namely from sewage. In other words, we can measure E.coli in water to understand if wastewater and stormwater has polluted a water body. E.coli is primarily used to monitor levels of faecal contamination in freshwater.
Water quality is like the weather. It can change quickly and frequently, so monitoring for E.coli and other faecal coliforms at the beach needs to be done frequently.
Guidelines for monitoring E. coli at beaches, rivers, lakes, and swimming holes were developed based on epidemiological evidence. This science relates the concentrations of these feacal coliform bacteria to the incidence of swimming-associated gastrointestinal illness, such as diarrhea, observed among swimmers.
How can we measure health risks at the beach using E.coli?
The concentration of E.coli in a water sample is typically measured per 100ml. Methods to measure E.coli include membrane filtration (CFU), multi tube fermentation (MPN), and more rapid processing methods like qPCR methods.
In Canada, the federal government guidelines, Guidelines for Canadian Recreational Water Quality, for E.coli are the following
E.coli Guidelines for Primary-Contact Recreation∗
Geometric mean concentration (minimum 5 samples) ≤ 200 E. coli /100 mL
Single sample maximum concentration ≤ 400 E. coli /100 mL
Countries, states, and provinces have their own standards and protocols, but most are very similar when it comes to quantifying E.coli at the beach.
E.coli Sample Collection and Processing Protocol
There are many sample collection and processing methods available for quantifying E.coli concentration in water. However, to date, most require a laboratory for processing results.
The most common methods for measuring the concentration of E.coli in water bodies are :
Multi Tube fermentation, such as IDEXX Laboratories colilert methods.
Quantitative Polymerase Chain Reaction (qPCR)
These are known as “persistent” methods, and they enumerate the number of E.coli in the samples. Results from these methods are available between 4 to 48 hours.
Models for predicting the concentration of E.coli at beaches and other recreational water sites are also used to forecast water quality. These models work just like weather forecasting does. Using historical water quality data, current and historical weather data, and other parameters such as geography and currents, the water quality can be forecasted. Predictive models are able to offer information to beachgoers about what is happening right now, and can even forecast up to two days ahead.
Water Rangers does not currently include a field test for E.coli for this in our kit. While many people are working on more portable tests, as it stands, this test can only be processed in a lab.
Testing for E.coli in recreational waters
Monitoring E.coli in the water is not a field test. If you are interested in monitoring E.coli, you will need to collect water and process the sample at a lab. You’ll need your own in-house lab to process sample results, or you can consider bringing your samples to a local environmental lab.
Public Health Ontario provides a helpful sample collection, handling, and processing guide.