Decision support tool

Control measures


Validation is an investigative activity to identify the effectiveness of a control measure, e.g. if the control of cyanobacterial growth in a waterbody or the prevention of break-through of cyanotoxins into the drinking water is being achieved, as desired. Validation is not intended for day-to-day management, but is typically intensive when a system is initially constructed or a new measure is implemented. It should be repeated periodically, but particularly after changes in the system are undertaken.

Validation begins with considering the data and information which already exist, e.g. from the scientific literature, guidelines, regulations and their explanatory text, historical data, and – very important – your own operational experience.

Research on site, specific to the individual setting, is adequate for validation particularly where uncertainty is large as to whether or not a measure will “work” sufficiently well in this situation. Running intensified monitoring programmes during extreme blooms is particularly valuable for validation of the performance of control measures in situations of high load. If cyanotoxins are identified in the finished drinking-water after a cyanobacterial bloom, the whole system (and the Water Safety Plan as well) will need to be improved.

Specifically for cyanobacteria, it is important to note that some measures only show a time-delayed effect. For example, the reaction of nutrient-rich water bodies to reduced nutrient loads from the catchment is usually slow, and cyanobacterial biomass is often reduced only after certain threshold values in nutrient concentration have been undercut.

An outcome of validation may be a change in a control measure or its monitoring system, or confirmation that it is (still) adequate to ensure health protection from safety from potential cyanotoxin exposure.

Your validation activities should be documented together with the results of your validation. With such documentation, you can demonstrate having observed your duties of due diligence towards the public surveillance agency responsible for your setting, and also towards journalists and the general public in case questions or incidents arise.

Examples of the validation of measures from catchment to drinking water treatment are given here.

Part of system Examples of measure Examples of validation
At different sites in the supply system (e.g. in the water body, filter drain, etc.) Continuous monitoring of cyanobacteria using turbidity or pigment fluorescence as indicators of cyanobacterial abundance. Validation of whether monitor signals adequately indicate cyanobacterial occurrence in your specific setting by performing cyanobacterial cell counts and/or biovolume determination. This may be different for different parts of the supply chain, e.g. for raw water and for filter outlets, and separate validation may be adequate.
Catchment Management measures to reduce nutrient loads by e.g. use restriction. Validate whether the measures implemented actually meet the targets set for nutrient load reduction by running specific research programmes to determine the load, e.g. by sampling tributaries under normal conditions and during heavy precipitation, or snowmelt events, and modeling nutrient budgets.
Water body Artificial mixing and/or biological measures to reduce cyanobacterial growth in a water-body. Monitoring of cyanobacterial growth, e.g. by weekly or fortnightly determination of biovolume (or other indicators of cyanobacterial biomass) and comparison of results with previous investigations at the same time of year.
Raw water abstraction Choice of offtake depths to minimise intake of cyanobacteria. Weekly or fortnightly determination of depth profiles of cyanobacterial occurrence, e.g. by determination of biovolume or in situ fluorescence, in a range of different situations of cyanobacterial occurrence and compare your plan for the selection of offtake depths to these findings.
Drinking water treatment Dosing of oxidant to remove, or of powdered activated carbon (PAC) to bind dissolved cyanotoxins. Evaluation of the amount needed at minimum to ensure cyanotoxin degradation / binding even in situations in which the system is challenged by high levels of competing organic carbon, as is the case during a cyanobacterial bloom. Such data may result in a scheme for dosing in relation to some indicator of cyanobacterial abundance that proves most useful to you, e.g. pigment fluorescence, biovolume or chlorophyll-a concentration analysis in the raw water.