2.2 Describe the water supply / recreational system

A thorough understanding of the system – from the catchment to the point of exposure – is the basis for analysing hazards and assessing risks. A flow diagram may be very helpful for visualisation. Specifically for cyanotoxins this includes the following:

è -Note: Often, not all of this information will be available. Following the motto: “It’s important to get started”, note these gaps in your worksheet, but do a first iteration of going through the rest of this decision support tool anyway to find out which information gaps are crucial for the decisions you need to make.

· a description of the catchment, i.e. its delineation, map of tributaries, discharge of tributaries (if available) geographic and hydrological characterisation such as area, slope, soil types, drainage systems

· land use, e.g. areas covered by forest, settlements, agriculture

· estimates of nutrient loads from agriculture: while sophisticated modelling may provide excellent load calculations, visual inspection may be a highly effective first step; furthermore it is necessary also for modelling in order to validate assumptions used in a model

· estimates of nutrient loads from sewage: this is possible from data on the size of the population connected to a given system and the type of treatment; in EU countries data on effluent amounts and concentrations should be available from treatment plant operators

· For reservoirs: morphometry, retention time, thermal mixing regime, site(s) and depth(s) of drinking-water offtake

· For rivers: flow and discharge; site of drinking-water offtake

· For the water-body: water quality data, particularly nutrient concentrations, Secchi disk transparency, phytoplankton population data; potentially also data on populations at higher trophic levels as these may impact on phytoplankton population structure and biomass.

· If available, data on cyanobacterial and cyanotoxin occurrence and any indication of human or animal illness from these

· If used as drinking-water resource: drinking-water treatment: which steps does the treatment train include (e.g. pre-oxidation, flocculation, sedimentation, filtration, ozonation, GAC filtration, slow sand or riverbank filtration, disinfection, … ), amount of water produced

· If used as drinking-water resource: distribution system: map of mains, reservoirs in the system including their condition and retention time (this may be relevant for cyanotoxin degradation in the mains)

It is of critical importance to validate such a description of the system by periodic inspection.

è Document your description of your system, e.g. in the worksheet provided on the starting page of this decision support tool.

è continue to step 3 – describe water use and users