Agua SALud: Water
Quality Analysis
Microbial Indicators of water quality
The use of normal intestinal
organisms (bacteria) as indicators of fecal pollution rather than pathogens
themselves is universally accepted for the monitoring and assessing the microbial
safety of water supplies[i].
The membrane filtration (MF) method was used to determine the amount of total
coliforms (TC) and Escherichia coli
in water samples, measured as colony forming units per 100 milliliters
(CFU/100ml). This method utilizes m-ColiBlue24™
broth to distinguish between E. coli
and total coliform based on the presence of a particular enzyme
(β-glucuronidase).
Microbiological samples were
collected in 125ml bottles from both communal water sources and from individual
households where children under five were living.
After collection, samples
were placed in a cooler with ice and filtered within 6 to 12 hours. During
filtration, 100ml of the sample was vacuum-filtered through a 0.45-μm
nitrocellulose membrane. The filter was transferred to a petri plate containing
an absorbent pad saturated with 2ml of m-Coli Blue24-Broth™. The filter was
incubated at 35°C +/- 2°C for 24 hours. Total coliforms were evidenced by the
appearance of red and blue colonies, whereas the blue colonies were specifically
E. coli.
Temperature, pH, Conductivity and Total Dissolved
Solids
At each water source:
temperature, pH, electrical conductivity, and total dissolved solids were
measured using a handheld combo meter (Hanna Instruments 98130). In addition
GPS coordinates were recorded at every collection site.
Sodium
Although conductivity was
used as an onsite indicator of salt concentration, samples were analyzed in the
Mexican National Commission of Water laboratory. Sodium (Na+)
content was assessed using a Corning™-412 Flame Photometer. Calibration curves
were generated by analyzing standards of 10, 20, 30, 50, and 100 ppm Na+
prepared from a NaCl stock solution.
Distilled water was used as a blank (0 ppm). Sodium content of water samples was then extrapolated based on
the calibration curves.
Arsenic Field Kit
Arsenic was measured using
the Arsenic Quick field test kit from
Industrial Test Systems (ITS). Following the sequential addition of three
reagents (tartaric acid, a separate oxidizer, and zinc powder), the arsenic
concentration of a sample can be measured based on the reaction of arsine gas
and a colorimetric test strip coated with mercuric bromide. The test procedure
is designed to detect inorganic arsenic As+3 and As+5.
The field test kit measurements
were validated with several samples analyzed at a lab at the University of
Washington following standard procedures.
Nitrate Field Kit
Nitrate in water sources was
measured using a Chemetrics field test kit based on the cadmium reduction
method. In the former, nitrate is
reduced to nitrite using cadmium as the reducing agent. The resulting nitrite
reacts to form a pink azo dye which is measured colorimetrically in a range
between 0 and 5 ppm.