DRINKING WATER GUIDELINES (WHO 2006)
Water contaminated with human or animal feces can lead to infection. The pathogens that are transmitted through contaminated through contaminated drinking water.
Of these, legionella, non-tuberculous mycobacteria, adenovirus can be transmitted through aerosols whereas acanthamoeba, aeromonas, non-tuberculous mycobacteria, leptospira, pseudomonas aeruginosa and schistosoma are transmitted through bathing and contact with mucus membranes, abraded skin or eyes. Rest all are transmitted through ingestion.
Balantidium coli, certain helminthes (Fasciola, Fasciolopsis, Echinococcus, Spirometra, Ascaris, Trichuris, Toxocara, Necator, Ancylostoma, Strongyloides and Taenia solium) are transmitted through food contaminated with faeces.
Microbial growth in water
After leaving the body of their host, most pathogens lose viability and the ability to infect. However common waterborne pathogens and parasites are those that have high infectivity and either can proliferate in water or possess high resistance to decay outside the body. Viruses, cysts, oocysts, ova are unable to multiply in water.
Processes to reduce bacteria, viruses and protozoa in water include, filtration coagulation, sedimentation, flocculation, lime softening, membrane filtration-ultrafiltration, Nanofiltration and reverse osmosis, disinfection by chlorine, ozone treatment and UV irradiation. Of these backside infiltration, membrane filtration with ultrafiltration, nanofiltration and reverse osmosis, result in removal of pathogens from 99% - 100%. UV irradiation results in 99% inactivation of bacteria, viruses and giardia and cryptosporidium. Ion exchange does not remove any pathogens. Disinfection does not remove cryptosporidium and has limitations against some viruses. It is also unsatisfactory against pathogens within flocks or particles.
For drinking water either directly intended for drinking or in distribution system E. coli or thermotolerant coli form bacteria should not be detectable in any 100 ml sample.
Chemical hazards in drinking water
There are many chemicals that may occur in drinking water, however only a few are of immediate health concern in any given circumstance. Exposure to high levels of fluoride which occurs naturally can lead to mottling of teeth and skeletal florosis. Similarly arsenic may occur naturally can increases risk of cancer and skin lesions. Other naturally occurring chemicals include uranium, selenium. Presence of nitrates and nitrites in water (arise from excessive application of fertilizers) has been associated with methemoglobinemia especially in bottle fed infants. Acidic or hard water can erode lead in lead pipes and increase lead levels in drinking water.
Treatment consists of chlorination, filtration, aeration, chemical coagulation, granular activated carbon treatment, ion exchange, ozonation, advanced oxidation processes and membrane treatment.
Radionuclide exposure in drinking water
It is very small under normal circumstances but may become contaminated by accidental release of radioactive substances in environment.
Guidelines for Drinking-water Quality. World Health Organization. Geneva, 2006.
Last Updated: 1st August 2009
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