First exploratory test sample taken below Marsh Lock

 

I went out on Tuesday 10th March with the HoTWater group to take a parallel sample of river water.

The results were that we agreed the pollution level was low, and both got readings below 500 cfu/100ml which would be classified as “Excellent”.

The HoTWater group use Fluidion Alert 1 technology to test water, and this device often returns higher numbers because it can detect particle-associated E. coli that other systems may miss. It returned a figure of 253 cfu/100ml.

The 3 x 1ml R-Cards on the other hand only detected a single instance of E. coli on 1 of the cards. This equates to 33 cfu/100ml.

Of course finding a single colony raises questions about detection sensitivity at low concentrations, but if one looks at the “Sufficient/Excellent” boundary of 500, it would mean that there would need to be fewer than 5 blue dots per R-Card, and the “Sufficient/Poor” boundary of 900 equates to an average of 9 blue dots per R-Card, thresholds that translate into dot counts robust enough to be reliably detected.

Given this detection sensitivity, I would record the actual figure, but present any R-Card reading below 100 as “<100 cfu/100ml” in the HoTWater app.