The level of risk for the users that is associated with chlorate formation in the WDN is strictly related to the amount of chlorate that is already present in drinking water from the WTP, i.e., to the input chlorate concentration. Most countries have not imposed any restrictions on maximum chlorate concentration in drinking water yet. Hence, the value of 700 μg/L suggested by the WHO guidelines for drinking water quality (WHO 2011) is here considered as a reference level to assess the relevance of chlorate build-up. The calculated increments in chlorate concentrations were hence compared to the WHO reference level, and the resulting values are reported in Table 4 for the different raw water types and tank mixing scenarios. The relative increments vary within a relatively narrow range, comprising between 0.4 and 6.7% of the WHO threshold value. The highest values always occur at the tanks in LIFO scenarios, and correspond to 5.9, 6.7, and 3.3% when the raw water source is represented by groundwater, surface water, and mixed water, respectively. Beside tanks, the maximum relative increments at WDN nodes can be found in the FIFO and, to a slightly lower extent, in the Mixed scenario (4.0%, 4.6%, and 2.9% for groundwater, surface water, and mixed water, respectively).

Table 4

Relative increments (%) of chlorate concentrations with respect to the reference value of 700 μg/L (WHO 2011)

 ClO3 increments [%]
GW source
SW source
Mixed source
MixedFIFOLIFOMixedFIFOLIFOMixedFIFOLIFO
Node 20 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 
Node 30 0.6 0.6 0.6 0.8 0.8 0.8 1.3 1.3 1.3 
Node 40 0.9 0.9 0.9 1.1 1.1 1.1 1.6 1.6 1.6 
Node 50 1.0 1.0 1.0 1.3 1.3 1.3 1.7 1.7 1.7 
Node 60 3.9 4.0 1.6 4.6 4.6 2.0 2.9 2.9 2.1 
Node 70 0.4 0.4 0.4 0.4 0.4 0.4 1.0 1.0 1.0 
Node 80 3.6 3.6 1.7 4.2 4.3 2.0 2.8 2.8 2.1 
Node 90 3.0 3.1 1.2 3.5 3.6 1.5 2.6 2.7 1.8 
Node 100 0.6 0.6 0.6 0.8 0.8 0.8 1.3 1.33 1.3 
Node 110 0.4 0.4 0.4 0.5 0.5 0.5 1.0 1.0 1.0 
Node 120 0.7 0.7 0.7 0.9 0.9 0.9 1.4 1.4 1.4 
Node 130 2.2 2.5 1.9 2.7 3.0 2.3 2.4 2.5 2.2 
Node 140 3.1 3.1 1.7 3.6 3.6 2.1 2.7 2.7 2.1 
Node 150 2.8 2.8 1.7 3.3 3.3 2.1 2.6 2.6 2.1 
Node 160 2.3 2.5 2.0 2.7 3.0 2.4 2.4 2.5 2.3 
Node 170 2.9 2.9 1.9 3.4 3.5 2.3 2.6 2.6 2.2 
Tank 65 4.7 5.0 5.6 5.4 5.6 6.4 3.1 3.1 3.3 
Tank 165 2.8 2.8 5.9 3.3 3.3 6.7 2.6 2.6 3.3 
 ClO3 increments [%]
GW source
SW source
Mixed source
MixedFIFOLIFOMixedFIFOLIFOMixedFIFOLIFO
Node 20 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 
Node 30 0.6 0.6 0.6 0.8 0.8 0.8 1.3 1.3 1.3 
Node 40 0.9 0.9 0.9 1.1 1.1 1.1 1.6 1.6 1.6 
Node 50 1.0 1.0 1.0 1.3 1.3 1.3 1.7 1.7 1.7 
Node 60 3.9 4.0 1.6 4.6 4.6 2.0 2.9 2.9 2.1 
Node 70 0.4 0.4 0.4 0.4 0.4 0.4 1.0 1.0 1.0 
Node 80 3.6 3.6 1.7 4.2 4.3 2.0 2.8 2.8 2.1 
Node 90 3.0 3.1 1.2 3.5 3.6 1.5 2.6 2.7 1.8 
Node 100 0.6 0.6 0.6 0.8 0.8 0.8 1.3 1.33 1.3 
Node 110 0.4 0.4 0.4 0.5 0.5 0.5 1.0 1.0 1.0 
Node 120 0.7 0.7 0.7 0.9 0.9 0.9 1.4 1.4 1.4 
Node 130 2.2 2.5 1.9 2.7 3.0 2.3 2.4 2.5 2.2 
Node 140 3.1 3.1 1.7 3.6 3.6 2.1 2.7 2.7 2.1 
Node 150 2.8 2.8 1.7 3.3 3.3 2.1 2.6 2.6 2.1 
Node 160 2.3 2.5 2.0 2.7 3.0 2.4 2.4 2.5 2.3 
Node 170 2.9 2.9 1.9 3.4 3.5 2.3 2.6 2.6 2.2 
Tank 65 4.7 5.0 5.6 5.4 5.6 6.4 3.1 3.1 3.3 
Tank 165 2.8 2.8 5.9 3.3 3.3 6.7 2.6 2.6 3.3 

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