MIT OpenCourseWare http ocw mit edu 11 479J 1 851J Water and Sanitation Infrastructure in Developing Countries Spring 2007 For information about citing these materials or our Terms of Use visit http ocw mit edu terms Water Quality Susan Murcott Water and Sanitation Infrastructure in Developing Countries Week 6 11 479 J 1 851J March 13 2007 Outline Does Improved Safe Two Safe Water Definitions Four Water Quality Categories Water Quality Lab Bacterial Indicators Turbidity Residual Chlorine EPA MWRA Water Quality Regulations Vietnam Water Quality Regulations Are Improved Drinking Water Supplies Safe Gundry et al 2006 Rural South Africa and Zimbabwe Randomized study 254 children aged 1 2 years Dry and wet seasons 10 CFU 100ml E coli Improved standpipe borehole protected well Unimproved unprotected well spring river canal At Source 12 71 Household Storage 41 81 Drinking Cup 51 82 Safe Water Definition We define safe drinking water as water that is safe to drink and available in sufficient quantities for hygienic purposes UN Millennium Task Force 2005 Safe Water Definition WHO GDWQ 3rd Ed Safe drinking water as defined by the Guidelines does not represent any significant risk to health over the lifetime of consumption including different sensitivities that may occur between life stages p 1 Those at greatest risk of waterborne disease are infants and young children people who are debilitated or living under unsanitary conditions and the elderly p 1 The judgment of safety or what is a tolerable risk in particular circumstances is a matter in which society as a whole has a role to play The final judgment as to whether the benefit resulting from the adoption of any of the health based targets justifies the cost is for each country to decide p 37 Water Quality 4 Broad Categories Microbiological Chemical Bacteria Organic Inorganic Viruses Naturally occurring Protozoa Anthropogenic Helminthes Physical Aesthetic Turbidity Odor Taste Appearance other Radionuclides Radium Uranium Radon Microbiological Contaminants Infectious diseases cased by pathogenic bacteria viruses protozoa and helminthes are the most common and widespread health risk associated with drinking water WHO 2004 Guidelines For Drinking Water Quality 3rd Ed p 123 Indicator Organisms Organisms whose presence indicate likely occurrence of waterborne pathogens indicator fecal contamination pathogen disease Ideal indicators should fulfill several criteria Always be present when pathogens are present Share similar persistence and growth characteristics Exist in larger concentrations for easy detection Detection tests should be relatively simple inexpensive Detection tests should detect indicator org only Detection tests should be applicable to all types of water Pathogens vs Indicator Organisms Pathogens Indicator Organisms Cause disease directly Most are not pathogenic Great variety Specific target groups Difficult to isolate Easy to detect and enumerate usually within 24 48hrs Takes longer to detect Some are opportunistic Note Direct detection of pathogens is inappropriate for routine water monitoring because based on methods available today it is complex timeconsuming and expensive Instead frequent and simple indicator tests are better especially when contamination can be intermittent and or undetectable What are coliforms WHO GDWQ 3rd Ed Gram negative rod shaped bacteria grown in bile salts fermenting lactose at 35 37 C producing acid gas and aldehyde within 24 48hrs oxidase negative non spore forming display galactosidase activity Operational not taxonomic definition First introduced 120 years ago based on its quantifiable relationship with potential health risks Risk of illness 0 100 Figure by MIT OpenCourseWare 0 010 0 001 0 000 10 1 100 103 104 4 9x102 5 8x103 101 102 Salmonella litre 103 104 105 106 Coliform MPN 100mL 107 108 7 2x106 7 1x107 6 5x104 7 0x105 Faecal coliform MPN 100mL Relationship between pathogen and coliform Olson Nagy 1984 Coliform Indicator Organisms The coliform group is the most common indicator group used in the world It includes Total Coliform Thermotolerant coliform formerly known as fecal E Coli Fecal coliforms are nowadays more properly referred to as thermotolerant coliforms Thermotolerant coliform are those able to ferment lactose at 44 45 C The namechange is due to the fact that some in this group may be of non fecal origin For example in tropical areas total coliforms can originate from decaying vegetation and do not necessarily indicate the presence of pathogens in water Still these indicators are used in the tropics due to lack of better methods Fecal streptococci and clostridia are other bacterial indicator groups commonly used in temperate climates E coli Exclusively fecal in origin WHO defn Thermotolerant coliforms with indole production and beta glucuronidase activity and absence of urease activity Constitutes 90 95 of the coliform bacterial in mammalian fecal material Most sensitive and specific indicator of fecal pollution currently available as well as most widely used world wide WHO Guideline Value for Verification of Microbial Water Quality from GDWQ 3rd Edition E coli or thermotolerant coliform bacteria must not be detected in any 100 ml sample for all water directly intended for Drinking Treated water entering the distribution system Treated water in the distribution system From Table 7 7 p 143 See also Table 5 2 p 97 E coli Grading Schemes In many developing and developed countries a high proportion of small community drinking water systems fail to meet requirements for water safety In such circumstances it is important to set realistic goals and classify water quality results in terms of an overall grading systems as illustrated here WHO GDWQ 3rd Ed 2004 p 97 Proportion of Samples Negative for E coli Population Size Water Quality 5000 5 000 100 000 100 000 Excellent 90 95 99 Good 80 90 95 Fair 70 85 90 Poor 60 80 85 Thermotolerant Fecal Bacteria Risk Categories for Untreated Rural Water Supplies Count per 100ml 0 1 10 10 100 100 1000 1000 Risk Category Conforms with WHO Guidelines Low Risk Intermediate Risk High Risk Very High Risk WHO Guidelines for Drinking Water Quality 2nd Ed Vol III Surveillance and Control of Community Supplies Geneva 1997 Why coliforms are imperfect indicators 1 Coliforms regrow or are suppressed in the environment In enriched waters even chlorinated sewage on biofilms in distribution systems E coli is 2 400 times more resistant to chlorine when attached