Summary of Week 2 of Introduction to Household Water Treatment and Safe Storage (Coursera – École Polytechnique Fédérale de Lausanne)
In water treatment (and in life), the question is what level of risk is acceptable. WHO defines safe drinking water as water that presents no significant risk to health over a lifetime of consumption.
The water safety framework comprises health-based targets, water safety plans and verification. Health-based targets include performance measures in terms of log reduction values.
It is important to note that measuring water quality is not the same as water safety because water quality varies in space and time, and no E.coli does not mean no contamination. Multiple treatment barriers should be put in place to remove contaminants.
Health-based targets include performance measures in terms of log reduction values. Water quality measurement does not mean water safety because water quality is variable in space and time, and no E.coli does not mean no contamination
Water treatment options: Sedimentation and filtration
A household-level treatment process typically comprises sedimentation, filtration, disinfection and safe storage.
- Sedimentation removes turbidity (suspended particles in water), and some pathogens. Turbidity itself has no health risks, but has impacts on subsequent treatment steps. Mechanisms include gravity settling, and coagulation and flocculation.
- Membrane filtration works on size exclusion, electrostatic effects and biological activity.
- Ceramic filters work on physical and electrostatic removal. It is common to brush silver onto filters, which contributes to bacteria reduction and prevents biofilm growth and clogging.
- Biosand filtration also uses size exclusion, electrostatic effects and biological activity.