Under Royal Decree 1085/2024, Spain has renewed its regulations on the use of reclaimed water, in line with the European Union’s Water Reuse Regulation 741/2020. This now broadens the scope of using reclaimed water across various sectors within the country.

Reclaimed water must be tested for bacterial contamination before use, and the decree specifies in Part C - Microbiological analysis methods – water quality the use of the most probable number method ISO 9308-2 (Colilert®-18) as a permitted method for the detection of E. coli. This means that accredited laboratories using Colilert-18 will be allowed to perform E. coli monitoring on reused water at the frequency defined by the new decree.

The European Union’s Re-Use Water Directive Regulation 2020/741 states that:

“The water resources of the Union are increasingly coming under pressure, leading to water scarcity and a deterioration in water quality. In particular, climate change, unpredictable weather patterns and drought are contributing significantly to the strain on the availability of freshwater, arising from urban development and agriculture. The Union’s ability to respond to the increasing pressures on water resources could be improved by wider reuse of treated waste water, limiting extraction from surface water bodies and groundwater bodies, reducing the impact of discharge of treated waste water into water bodies, and promoting water savings through multiple uses for urban waste water, while ensuring a high level of environmental protection.”

The IDEXX Colilert-18 method uses liquid culture and offers an easy and rapid solution for detecting E. coli and coliform bacteria in drinking water. No agar preparation is necessary, the reagent comes pre-weighed and contains no toxic compounds. Samples can be processed in less than one minute and confirmed results are available after 18 hours incubation. Interpretation of results is achieved through observable change of colour after incubation. Combining Colilert-18 with Quanti-Tray provides easy, rapid, and accurate bacterial counts, delivering semi-automated quantification based on the most probable number (MPN) model.

Colilert-18 has been trusted by water utilities worldwide for more than 20 years, and in 2012, the Colilert-18/Quanti-Tray® method became the ISO standard 9308-2. It is also specified as a reference method in the European Drinking Water Directive 2020/2184.

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