generally much faster in marine and estuarine waters than freshwater [40, 41]. Exposure of bacteria to sunlight is one of the most important factors causing bacteria
die-off, while different treatment processes of surface water can significantly affect
die-off of bacteria. Table 3.20 summarizes comparison of die-off rates and treatment
effectiveness for different microbes.
Is the water body used for contact recreation?
Sanitary inspection category
Classification
Microbial water quality assessment
Very poor
Water subject to occasional and
predictable deterioration*
Poor
Fair
Good
Very good
Very good (but unsuitable
for several days after rain)
Good (but unsuitable for
several days after rain)
Fair (but unsuitable for
several days after rain)
Unclassified (reassess if usage changes)
NO
YES
Fig. 3.14 Simplified framework for assessing surface (recreational) water environments
100
10
Percent Remaining
1
0
1
2
Reaction Time - days
K = 1.50
K = 1.00
K = 0.50
3
4
5
Fig. 3.15 Effect of different die-off rates (k) on bacteria mortality [39]
3 Surface Water Quality and Analysis
109