4.3. Variability between wards
Each ward has different operations, infrastructure, and envi-ronments that could affect water quality; therefore, it is useful
to compare water quality between wards. The spatial distri-bution of total coliform concentrations in tap samples shows
this heterogeneity (Fig. 4). These data suggest that water
quality in both IWS and 24 7 wards was highly dependent on
local factors.
Ward 10, which had the highest percentage of samples
positive for total coliform among 24 7 wards ( Fig. 5 ), is
adjacent to ward 11 ( Fig. 4 ), which had the lowest percent of
positive samples (Fig. 5). Given that source water quality and
water distribution system infrastructure should be similar in
24 7 wards, the differences were likely due to the local
environment or operational factors in wards 10 and 11.
A similar percentage of samples were positive for total
coliform with similar concentrations in IWS wards 14 and 25
as in 24 7 ward 10, illustrating that IWS can potentially
provide water with similar levels of indicator bacteria as 24 7
(similar trends were observed with E. coli; data not shown)
( Fig. 5). Differences in the percent of samples with > 0.2 mg/L
free chlorine could not explain the total coliform results,
except that the IWS wards where total coliform was detected
more frequently also had persistent low or non-detectable
chlorine (Fig. 5).