Finding faecal bacteria in water

Published: 21 September 2018

When the temperature rises, people want to go for a swim or take their children to a water playground. Unfortunately, the water can sometimes be infected with faecal bacteria. Time for a change of plan. No water fun today! To find out faster whether water is safe, a new detection method is being developed that identifies faecal bacteria using DNA.

Dutch provincial authorities are responsible for monitoring natural bathing water. They check water quality regularly by measuring levels of E.coli to decide whether the water is safe for bathing. The information can be found on  The number of warnings about bathing water has doubled over the past two years. On top of all that, people don’t always check the website first, they may bathe in water that hasn’t been checked, or checked less often, and they may swim outside the summer season (May-October).  And so there is still a risk of infection. Monitoring is needed in more places, more often and faster. However, it is expensive to check every location and it is almost impossible using current methods.

Trials with faster test

Until recently, a culture had to be made with a water sample to identify E.coli. That means using a laboratory and it takes time. And during that time, it’s impossible to draw firm conclusions about water quality. The fast test that Deltares is now trying out with water authorities and their laboratories can identify E.coli within ninety minutes. The test doesn’t require a laboratory technician or water quality expert. After a short course, anyone can measure and assess the water quality. The measuring equipment fits in a bag. And it can be used for fresh, brackish and salt water.

Identifying bacterial DNA

After a short pre-treatment phase, the water sample is placed in a device that identifies E. coli DNA. This new approach (mobile qPCR) is now being tested in practice. In the near future, it will allow municipal authorities or managers of marinas, owners of beach pavilions and water playgrounds or event organizers to measure water quality. More measurements become possible and bathers will be warned sooner when there is a problem with the water quality. In the Netherlands recently, the Amsterdam City Swim was cancelled when measurements with the new method were made after unexpected heavy rain.

In addition to E.coli

The device for the DNA test has just been brought onto the market and it costs approximately 4000 euros. In addition to E.coli , it can also be used to identify other bacteria such as Weil’s disease (Leptospirosis) and Legionella.