Decision support tool


Verification confirms that with the measures in place and implemented, the water quality targets (e.g. drinking or bathing water ordinance) are being achieved. In practice, this means monitoring cyanotoxin concentrations in finished drinking-water or cyanobacterial biomass and/or cyanotxins at recreational sites. Meeting the targets assures that the whole system is working safely and people are not being exposed to cyanotoxins.

Developing a verification scheme for your setting requires consideration of the adequacy of the selected time intervals and sampling sites in relation to heath risks from potential cyanotoxin exposure that you assessed for your setting. For example, more cyanotoxin analyses are necessary during cyanobacterial mass development in summer, while in winter these can usually be omitted in temperate zones, except during – occasionally observed – year-round presence of Planktothrix rubescens in reservoirs. For bank filtration or artificial recharge, cyanotoxin analyses should be intensified for several weeks when the water with the highest cyanobacterial abundance is expected to reach the wells (in temperate zones this is more likely in winter). In addition, cyanobacterial biomass may be highly variable in a water body due to changing wind direction and speed and may thus require – depending on the main water use – increased sampling frequencies, e.g. at bathing sites.

Your verification activities should also be documented in your Water Safety Plan. This covers the sampling sites and time intervals of sampling as well as the analytical methods used. Define responsibilities for the evaluation of the results, the maintenance of records and the resulting actions arising. With such documentation, you can demonstrate having observed your duties of due diligence towards the surveillance authority responsible for your setting, and also towards journalists and the general public in case questions or incidents arise.