4.2 Water Quality Assessment
Water from the main village sources (boreholes, springs, and rainwater harvesting systems) was
tested for fecal contamination, chlorine demand, arsenic, and nitrates. Basic measurements such
as pH and conductivity were also taken. Household water samples were also collected and
analyzed in order to trace the “history” of a sample of water—quality at the source, quality after
collection for household use but before preparation, and quality after preparation for drinking.
4.2.1 Methods
Fecal Contamination: The Colilert® testkit from IDEXX was used to estimate the levels of
total coliform and E. coli contamination in the water. One Colilert powder packet was added to a
100 mL sample and dissolved. The mixture was then poured into a Colilert tray, and the tray was
sealed with a travel iron. The samples were incubated for 24 hours at approximately 37°C in a
homemade incubator. The incubator was constructed from a cardboard box, Styrofoam, and hot
water bottles. After 24 hours the number of coliform organisms in the sample was estimated by
counting the number of bright yellow wells and matching that value to a most probable number
(MPN) table provided by IDEXX. The number of E. coli in the sample was estimated by
counting the number of wells that fluoresced blue when placed under a handheld, battery
operated UV light and matching that value to the MPN table.
Chlorine: Chlorine demand tests were performed by adding a known amount of chlorine (in the
form of diluted bleach) to a sample, and then measuring the amount of chlorine remaining in the
sample after 24 hours. The measurements were made by adding a chlorine indicator dye to
aliquots of the water samples and then recording the change in optical transmittance.
pH and Conductivity: The pH of water samples was measured in the field using pH indicator
strips. The conductivity was measured in the field by simply inserting a handheld, battery
operated conductivity probe.
Arsenic and Nitrates: The arsenic and nitrate measurements were performed at Duke University
using water samples that had been brought back from Uganda.
4.2.2 Results
Average Total Coliform and E. coli Counts
250
Most Probable Number (MPN) (organisms/100 mL)
Total Coliform Average
E. coli Average
200
150
100
50
0
Boreholes, n=4
Springs, n=3
Rainwater Tanks,
n=5
Source
Figure 1. Summary plot of fecal contamination results.
Household
Unprepared Water,
n=4
Household
Prepared Water,
n=7
Source Type
Source Location
Date
(2006)
Borehole
Borehole
Borehole
Borehole
Borehole
Borehole
Borehole
Borehole
Borehole
Borehole
Henry Hall
Henry Hall
Henry Hall
Kanoni
Kanoni
Ryumba
Kasaka
Kasaka
Kasaka
Kasaka
18-May
22-May
25-May
18-May
21-May
21-May
21-May
22-May
24-May
25-May
3.1
0
Spring
Katwekambwa
18-May
Katwekambwa- 1:100 dilution
Njabire
Njabire
Njabire
Kanoni-Maddu
21-May
21-May
24-May
26-May
23-May
165.2
38.4 to
50.4
3.1
<1
13.7
27.1
5.9
Spring
Spring
Spring
Spring
Spring
>200.5
118.4 to
200.5+
8.7
<1
17.8
>200.5
Tank
Kanoni-Maddu spring water
carried to and stored in tank
23-May
>200.5
18-May
21-May
24-May
22-May
Rain-Roof-Tank
Rain-Roof-Tank
Rain-Roof-Tank
Rain-Roof-Tank
Rain-Roof-Tank
Rain-Roof-Tank
Drinking
Drinking
Drinking
Drinking
Drinking
Drinking
Drinking
Drinking
Drinking
Drinking
Drinking
Drinking
Drinking
Kanoni Hospital
Kanoni Hospital
Kasaka house A
Kasaka house B
Primary School, Tank 1 (4 yrs
old)
Primary School, Tank 1 (new)
Kasaka house B prepared
water
Waterguard Bag Water
Kasaka house C boiled water
Kasaka house C boiled water
Kasaka house C unboiled
water
Kasaka house C unboiled
water
Kanoni-Maddu Bag Water
Kasaka Secondary School
Kettle
House along road-- boiled
water
Kasaka House D Unboiled
Kasaka House D Boiled
Kasaka House E Unboiled
Kasaka House E Boiled
Table 1. On site water quality measurements.
Coliforms
(MPN)
E. coli
(MPN)
<1
<1
3.1
7.5
<1
<1
<1
<1
1
<1
pH
Conductivity
(μS)
Chlorine
Used
(mg/L)
180
6
5.9
5.6
5.1
5.8
5.1
4.5
184
89
108
3.3
2.75
98
1.6
5.4
4.8
4.8
53
68
70
4.5
63
27.1
5.6
83
165.2
59.1
>200.5
>200.5
3.1
<1
>200.6
<1
7.5
6.9
6
6.1
79
29
37
25-May
25-May
>200.5
>200.5
>200.5
16.4
5.7
5.9
19
5
22-May
25-May
22-May
24-May
>200.5
<1
>200.5
<1
25.4
<1
>200.5
<1
6.3
84
22-May
>200.5
>200.5
24-May
23-May
<1
1
5.8
64
23-May
>200.5
>200.5
118.4 to
144.5
<1 to 2
7
77
24-May
25-May
26-May
27-May
28-May
>200.5
>200.6
>200.7
>200.8
>200.9
<1
7.5
<1
3.1
<1
6.1
5.8
6.7
30
6
29
4.25
4.98
3.4
rep1
rep2
rep3
rep4
Source
ug/L
ug/L
ug/L
ug/L
Kasaka borehole, filtered
-1.2
-1.3
na
na
Kasaka borehole, unfiltered
-1.9
-1.3
na
na
Kanoni hospital roof, filtered
Primary school rainwater tank,
filtered
0.2
-1.1
na
na
0.7
-1.5
na
na
Henry Hall, filtered
0.4
1.0
na
na
Kanoni spring, filtered
-0.6
-0.6
na
na
Njabire spring, filtered
-1.4
-1.5
na
na
Henry Hall, unfiltered
leaked out
-0.9
na
na
23.8 ppb external QC
24.6
24.8
25.6
24.3
Table 2. Arsenic measurements.
Source
Kasaka borehole, filtered
Kasaka borehole, unfiltered
Kanoni hospital roof, filtered
Primary school rainwater tank,
filtered
Henry Hall, filtered
Kanoni spring, filtered
Njabire spring, filtered
Henry Hall, unfiltered
Table 3. Nitrate measurements.
Nitrates (mg/L)
0.02
0.05
0.045
0.03
0.03
0.02
0.04
--
4.2.3 Interpretation of Water Quality Results
Fecal Contamination: As seen in Figure 1, the boreholes provide the only reliably
uncontaminated water. EPA standards require samples of drinking water to have an E. coli count
of zero, yet the water samples we collected from springs, rain water tanks, and unprepared
household sources had average counts of over 50 organisms per 100 mL. The average for
prepared water sources was lower (3.9), but still at an unsafe level. It is also important to note
that in some cases, water that was collected from an initially pure source—the boreholes—gets
contaminated with E. coli during collection or storage. This trend can be seen from the
“household unprepared water” bar in Figure 1, since each of the households sampled in that data
set gathered their water from a borehole that was shown to have no E. coli contamination.
Chlorine Demand: The chlorine demand varied from source to source, as seen in Table 1. This
was expected, since chlorine demand depends heavily on the turbidity of the water.
Arsenic and Nitrates: For all sources measured the arsenic and nitrate levels were below the
maximum allowable levels specified by the EPA (0.01 mg/L and 10 mg/L, respectively).
RECS/ FUTURE IDEAS/PROJECTS
-
Point of use purification system, since contamination sometimes occurs after collection
Chlorination, since it would provide longer lasting bacterial protection (as long as
adequate residual levels)
Flushing, filtering, cleaning, etc system to improve quality of rainwater harvested from
roofs.