Evaluation of the bacteriological quality of drinking water is done us - PDF document

1 Evaluation of the bacteriological qualit
Evaluation of the bacteriological quality of drinking water is done using “coliform” testing.Coliform bacteria are found in the intestinal tract of warm-blooded animals, surface water,some soils, and decaying vegetation. Coliform bacteria are used as “indicator” organisms.If they are present, pathogenic, or disease-causing organisms, could be present. TheMichigan Department of Environmental Quality (DEQ) laboratory and many privatelaboratories use the “defined substrate method.” A positive result may indicate that a watersupply is not properly protected from contamination. The “defined substrate method” alsodetects E. coli, an organism that always originates from mammal or bird intestinal tracts. IfE. coli is detected, it is more likely that the water supply may contain disease-causingorganisms resulting from fecal contamination. Result CodeThis means: ND“Not Detected” – No coliform organisms were detected in the water sample. The sample met the state drinking water standard for bacteriological qualityat the time of sampling. (Similar results may be reported as negative;absent; or zero, “0.”)POS – Coliform organisms were present in the water sample. Safety cannot be assured. Collection of a resample to confirm the original result isrecommended. An investigation into the cause of the problem by a qualifiedindividual is advised. (Similar results may be reported as present or anynumber from 1 to 200.)EC-POS“E. coli detected” – E. coli organisms were detected in the water sample. E. coli organisms are found in the intestines of warm-blooded animals, andas such, their presence in a water supply is considered an indication ofsewage contamination. Precautions are recommended in the use of thewater supply. These results are the same as fecal coliform positive;however, E. coli results indicate sewage contamination with more certainty.COMMENTSColiform organisms may die during sample holding time (time fromcollection to testing). The laboratory will comment that results may not berepresentative/valid if sample holding time is longer than 48 hours. Thefederal standard for a coliform holding time limit for public water supplies is30 hours. The DEQ laboratory analyzes eight commonly requestedparameters in a routine procedure called a “partial chemicalanalysis.” Below are two tables of these parameters andassociated problems. Table I lists three parameters wherethe USEPA and the state of Michigan have establisheddrinking water health advisory levels for public water supplies.Parameters listed in Table II are associated with aestheticwater quality problems.Test results are reported in milligrams per

2 liter (mg/l).TABLE I Nitrate asNitrogenN
liter (mg/l).TABLE I Nitrate asNitrogenND to 34 to 10Over 101(blue baby) esp. infants. Nitrite asNitrogenND to0.30.4 to 1Over 11(blue baby) esp. infants. Fluoride0.7 to1.2ND to 0.7or1.2 to 4Over 45Low levels are beneficial inpreventing tooth decay.High levels may causemottling of enamel. TABLE II ND to2020 to 250Over 250Taste, corrosion. Hardness50 to125125 to 250Over 250Scaling of water fixtures,soap scum at high levels,corrosion at low levels. IronND to0.20.2 to 0.3Over 0.3Staining, turbidity, taste,odor. ND to20Special diets may require water of low sodium content.Persons on severely restricted sodium diets shouldconsult with their physician regarding continued use ofthe water supply. Acceptability of sodium concentrationvaries with sensitivity to taste. SulfateND to5050 to 250Over 250Over 500Taste, odor, scaling inboilers & heat exchangers.May have laxative effectespecially for new supplyusers (traveler’s diarrhea). BACTERIOLOGICAL ANALYSIS RESULTS OF COLIFORM ANALYSIS PARTIAL CHEMICAL ANALYSIS 1 USEPA drinking water standard 2 See DEQ pamphlet EQC2033 “Nitrate in Drinking Water” 2/003 USEPA requires analysis within 48 hours4 Optimal range of fluoride concentration per American Dental Association5 USEPA drinking water standard is 4.0 mg/L for the state of Michigan UNDERSTANDINGYOUR DRINKINGWATER SAMPLE RESULTS For further information contact your local health department or theMichigan Department of Environmental QualityDrinking Water & Radiological Protection DivisionGround Water Supply SectionPO Box 30630Lansing, MI 48909-8130Phone: 517/241-1377Fax: 517/241-1328Internet address: www.deq.state.mi.us/dwr WATERSAMPLING ü Use a clean, indoor faucet. ü Try to avoid threaded taps, leakyor swing-type faucets.ü Do not use a dirty or contaminatedü Do not sample through a hose orü Always sample the cold water.ü Allow the water to run in a steadyü Do not set the bottle cap down.ü Do not touch the inside of the capü Do not allow the cap or bottle toü Do not rinse the bottle.ü Maintain a steady low-flow stream.ü Fill the container to the fill line. Donot overfill.ü Seal the container as soon as it isfilled.ü Enclose submission slip andü Send/transport samples to the labearly in the week. Unless your water well is properly designed, constructed, and maintained, a test resultconforming to state standards may give youa false sense of security. A defective wellbacteriological tests, but its continued safetycannot be assured.While coliform bacteria and partial chemicaltesting are good screening tools, they do notsolvents, heavy metals, herbicides andpesticides. More complex and expensiveYour local health department can assist youA WORD OFCAUTION... Phone: 517/485-9033 7/2001