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Water testing & Pasteurization in Africa
A guide to water testing without access to a laboratory, and how to pasteurize contaminated water using sunshine and a simple solar cooker.
Date(s): June 6, 2006. Album by Bob Metcalf. Photos by Bob Metcalf. 25 - 48 of 112 Total. 85635 Visits.
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Shake tube to dissolve chemicals

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Incubate tubes at 35°C for next day results

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Tubes can also be incubated next to one's body to obtain next day results.

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Next day Rresults Clear = no coliform bacteria. Yellow (ONPG+) = coliform bacteria present, possibly E. coli

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Use a battery-operated long UV light to shine on tubes. Blue fluorescence = MUG +, E. coli is present, water not safe to drink.

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The best test for E. coli in foods: E. coli Count Petrifilm

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Two substrates in Petrifilm for E. coli, lactose and BCIG

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To use Petrifilm, label sample source and time

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Use sterile pipette to collect exactly 1 ml of water

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Raise the edge of film to expose nutrient circle

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Add 1 ml of water sample to nutrient circle

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Carefully roll down film onto nutrient circle

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Use flat side of plastic spreader to gently distribute 1 ml over entire circle

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Petrifilms ready for incubation

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Petriflms covered with firm cardboard enables incubation on one's body, ~20 doublings for invisible bacteria to develop into visible colonies

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Results usually in 10-18 hr. E. coli = blue colonies with gas. Coliforms besides E. coli = red with gas.

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Petrifilm & Colilert tests correlate with risk of disease, WHO Guidelines for Drinking Water Quality, 2nd Edition.

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Ready to start workshop. Boniphace translates for Bob Metcalf

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Two water sources in Saka Saka. From a pump (green bucket) and an open stream (yellow bucket).

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Adults will sample either pump or stream water

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Mixing inoculated Colilert tubes, to incubate overnight

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Petrifilms also inoculated by either pump or stream water

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