There are more than 450 designated bathing waters across England. The Environment Agency is responsible for monitoring, improving, and maintaining water quality at all designated bathing waters. Importantly, designation also means that information is provided to the public to help inform decisions on where and when to bathe. Here, Environment Agency scientist Emily Egglestone explains how a bathing water sample is tested to see how clean it is.
I am a scientist at the Environment Agency’s lab in Starcross, near Exeter. I work in the Microbiology team, and from May to September, my main role is testing bathing water samples to check how clean the water is and provide the public with information so people can decide when and where to swim.
On average, we get about 50 – 100 samples come in each day from the designated bathing waters. We have a dedicated sampling team and courier system to sample sites across England. The water is kept in sterile bottles that are either 500ml or a litre in volume and are kept refrigerated until their arrival at the lab. The sample registration team arrive at about 6am each morning to register the samples so that the scientists can start their analysis at 7am.
I love the fact that not every day is the same. We know roughly how many bathing water samples are going to come in each day, but sometimes you can get an influx which will need managing. But I work in a great team that is really experienced and supportive, with a couple of colleagues who have worked here for more than 20 years!
At the lab, the samples will come to us on a trolley, normally 50 at a time. We put them in time order before starting the actual testing process. Each sample is analysed for two different types of bacteria, E. coli and intestinal enterococci. These are both gut bacteria and are good indicators of faecal pollution within the bathing water sites.
A certain volume of each sample is put through a filter paper. This lets the water pass through but captures the bacteria. The filter paper is then put onto specific growth media and incubated to allow the bacteria to grow. E. coli is incubated at 30°C for 4 hours followed by 44°C for 24 hours whereas intestinal enterococci take longer, it is incubated at 37°C for 4 hours and then 44°C for 48 hours. The lower starting temperature encourages the bacteria to grow and the higher temperature is more selective, promoting the growth of faecal gut bacteria.
Our work is very time sensitive. After 24 hours, we’re able to look at our results for E. coli. If E. coli is present in the sample, the plates will have blue-green colonies growing on them. We count those colonies and calculate how many were in the original sample. It is a similar process for the intestinal enterococci test, but these plates produce red colonies and the results are obtained 48 hours after filtration. The results then require further confirmation which takes the whole process to 72 hours. We report the results immediately so action can be taken to put in place the appropriate pollution prevention measures.
For most bathing water samples we see, the results come out clean. But if there is pollution present then it will show more colonies and more growth. River samples do tend to have higher concentrations of bacteria than coastal waters. Rivers are closer to sources of bacteria than the sea, and don’t have the benefit of dilution that occurs by the time bacteria reach the sea.
Once a bacterial result is obtained, for further investigations the lab can analyse the DNA in the sample to try to find the potential source of the faecal pollution, this is known as Microbial Source Tracking (MST). Examples of DNA we can detect are human, dog, birds or cows and sheep. This information can help investigators to get to the root cause of the issue and take action. Our data is used to put in place local action plans with partners to address pollution and can provide the public with vital information as to the cleanliness of bathing waters.
The results of water quality tests are uploaded onto our Swimfo website throughout the bathing season. Sample data is typically on Swimfo about five days after being taken. Here you can search by name or location to look at the water quality, as well as see any incidents or predictions of temporarily reduced water quality levels. You can also review whether a bathing water is classed as Excellent, Good, Sufficient or Poor. Samples tested by us throughout the bathing season are used to produce an annual bathing water classification. Four years' worth of data is used to make a classification, allowing us to identify trends and advise on appropriate pollution prevention measures.
I love the fact that I play a role in providing this information – from the bottles of water, to the small colonies that grow in the incubator, we’re able to help people make an informed decision on where to swim.
1 comment
Comment by Andrew Tyerman posted on
Thanks for the work you do Emily. Can you explain why there are two readings for Entrococci, a presumptive and a confirmed figure are listed? They are usually the same but not always. Why is that?
Thanks