Test 4 - Bacteriological Quality and Drinking Water Standards

Question 1 ప్రశ్న 1

Why are indicator organisms commonly used in the bacteriological assessment of drinking water instead of attempting to test routinely for every possible waterborne pathogen?

A Because pathogenic organisms can never occur in drinking water B Because suitable indicator organisms provide a practical means of detecting faecal contamination or treatment failure without individually testing for every pathogen C Because indicator organisms are always more dangerous than all pathogens D Because bacteriological analysis is intended only to determine water colour

Question 2 ప్రశ్న 2

Which organism is regarded as the most specific commonly used bacterial indicator of recent faecal contamination in drinking water?

A Escherichia coli B Nitrosomonas C Rhizobium D Thiobacillus

Question 3 ప్రశ్న 3

Which statement best distinguishes total coliform bacteria from E. coli in drinking-water interpretation?

A Total coliforms are necessarily all faecal pathogens, whereas E. coli is harmless environmental bacteria only B Total coliforms are a broader indicator group, while E. coli is more specifically associated with faecal contamination C E. coli is a chemical constituent and total coliforms are physical particles D There is no microbiological distinction between them

Question 4 ప్రశ్న 4

What is meant by thermotolerant coliform bacteria in traditional water-quality terminology?

A Coliform organisms capable of being detected under elevated incubation-temperature conditions historically used to indicate faecal contamination B Bacteria that survive only at freezing temperatures C All microorganisms that produce chlorine D Viruses capable of passing through a membrane filter

Question 5 ప్రశ్న 5

Under the current bacteriological requirement applied with IS 10500, what is the requirement for E. coli or thermotolerant coliform bacteria in water intended for drinking?

A Up to 100 organisms per 100 mL are acceptable B Up to 10 organisms per 100 mL are acceptable C They shall not be detectable in any 100 mL sample D Their presence is acceptable if turbidity is below 1 NTU

Question 6 ప్రశ్న 6

For treated water entering the distribution system, what is the current requirement for total coliform bacteria under the IS 10500 bacteriological framework?

A They shall not be detectable in a 100 mL sample B Up to 50 organisms per 100 mL are acceptable C Up to 10 organisms per 100 mL are acceptable if chlorine is present D No total-coliform testing is required

Question 7 ప్రశ్న 7

A 100 mL sample of treated drinking water is found to contain confirmed E. coli. Which interpretation is correct?

A The result is compliant because only one sample was tested B The result is acceptable if hardness is below 200 mg/L C The bacteriological requirement is not satisfied and faecal contamination must be suspected D The result affects only the taste of the water

Question 8 ప్రశ్న 8

Which statement correctly interprets a result in which no E. coli is detected in a 100 mL drinking-water sample?

A It proves that every possible bacterium, virus and protozoan pathogen is absent from the entire water supply B It satisfies the E. coli criterion for that sample but does not prove absolute absence of every possible pathogen C It proves that the water also satisfies every chemical standard D It means that disinfection is unnecessary

Question 9 ప్రశ్న 9

What is the principal significance of detecting total coliform bacteria in treated water within a distribution system when E. coli is not detected?

A It necessarily proves recent faecal contamination B It can indicate a problem with treatment effectiveness, regrowth, intrusion or distribution-system integrity and warrants investigation C It proves that the water contains excessive nitrate D It has no operational significance

Question 10 ప్రశ్న 10

What is the basic principle of the membrane-filtration method used for detecting and enumerating E. coli and coliform bacteria in suitable drinking-water samples?

A Water is evaporated completely and the remaining salts are weighed B A measured water volume is passed through a membrane that retains bacteria, and the membrane is cultured on an appropriate medium C Water pH is measured and converted directly to bacterial count D Chlorine demand is used as the bacterial population

Question 11 ప్రశ్న 11

Which current Indian Standard specifically covers membrane-filtration detection and enumeration of E. coli and coliform bacteria in water with low bacterial background flora?

A IS 456 B IS 15185:2016 C IS 800 D IS 1343

Question 12 ప్రశ్న 12

Why is membrane filtration particularly suitable for disinfected drinking water or other waters with relatively low bacterial background populations?

A Because the method can process a defined relatively large sample volume and directly recover target colonies on the membrane B Because it requires the water to contain very high suspended solids C Because the membrane chemically destroys all bacteria before counting D Because no incubation is required

Question 13 ప్రశ్న 13

A laboratory filters exactly 100 mL of treated drinking water and confirms three E. coli colonies on the membrane. What result and compliance interpretation follow?

A 3 CFU/100 mL and bacteriologically non-compliant B 0.03 CFU/100 mL and compliant C 300 CFU/100 mL and compliant D 3 mg/L and chemically non-compliant

Question 14 ప్రశ్న 14

A 50 mL water sample yields two confirmed E. coli colonies by membrane filtration. Assuming proportional reporting and no dilution, what is the equivalent result per 100 mL?

A 1 CFU/100 mL B 2 CFU/100 mL C 4 CFU/100 mL D 50 CFU/100 mL

Question 15 ప్రశ్న 15

What does the Most Probable Number method estimate in bacteriological water analysis?

A A statistically inferred concentration of indicator bacteria from the pattern of positive and negative culture tubes B The exact mass of bacteria in milligrams C The turbidity of water in NTU D The chloride concentration in mg/L

Question 16 ప్రశ్న 16

Which statement correctly distinguishes the MPN and membrane-filtration approaches?

A MPN is based on statistical interpretation of positive culture tubes, whereas membrane filtration permits colonies retained from a known water volume to be detected or enumerated on a membrane B Both methods determine only water hardness C Membrane filtration requires no microbiological culture D MPN directly weighs bacteria in grams

Question 17 ప్రశ్న 17

Why should a bacteriological water sample be collected aseptically in a sterile container?

A To prevent organisms introduced during sampling from producing a false indication of contamination B To increase the bacterial population before analysis C To change the sample pH to neutral D To remove dissolved solids from the sample

Question 18 ప్రశ్న 18

Why is sodium thiosulphate commonly provided in bacteriological sample bottles used for chlorinated drinking water?

A To neutralize residual chlorine so that it does not continue killing bacteria after the sample has been collected B To increase residual chlorine during transport C To increase turbidity so bacteria are easier to see D To convert E. coli into total dissolved solids

Question 19 ప్రశ్న 19

Which practice is most appropriate after collecting a bacteriological drinking-water sample?

A Analyse it as promptly as practicable under prescribed sample-preservation and transport conditions B Leave it open at room temperature for several days before testing C Add untreated sewage to maintain bacterial activity D Boil the sample before bacteriological examination

Question 20 ప్రశ్న 20

How can excessive turbidity adversely affect microbiological safety even when a disinfectant is applied?

A Particles can shield microorganisms and increase disinfectant demand, reducing effective disinfection B Turbidity automatically sterilizes water C Turbidity converts all pathogens into harmless dissolved salts D Turbidity has no relationship to treatment performance

Question 21 ప్రశ్న 21

Which statement about residual disinfectant and bacteriological quality is most appropriate?

A A disinfectant residual is an operational protective barrier, but its presence does not replace required bacteriological testing B Any measurable chlorine residual guarantees that E. coli is absent everywhere in the system C Residual disinfectant is itself a bacterium D Residual disinfectant is relevant only to wastewater

Question 22 ప్రశ్న 22

Why is E. coli detection in treated distribution water normally treated as more serious evidence of sanitary failure than detection of total coliforms alone?

A Because E. coli has a stronger and more specific association with faecal contamination B Because total coliforms are chemical contaminants C Because E. coli is measured only by pH D Because total coliforms can never occur in water

Question 23 ప్రశ్న 23

A treated-water sample entering a distribution system shows E. coli not detected but total coliforms detected. What is the most appropriate interpretation?

A The water automatically complies because E. coli alone matters B The water fails the treated-water total-coliform requirement and the treatment or sanitary integrity should be investigated C The result proves excessive fluoride D The result is acceptable if colour is unobjectionable

Question 24 ప్రశ్న 24

If repeated downstream samples in a distribution system show indicator bacteria while water leaving the treatment plant is consistently compliant, which engineering interpretation is most reasonable?

A Contamination or loss of sanitary integrity within storage or the distribution system should be investigated B The source water can be ignored completely C The laboratory must automatically be wrong D The result proves that hardness is excessive

Question 25 ప్రశ్న 25

Which statement correctly distinguishes bacteriological compliance from overall drinking-water compliance?

A Water can be considered fully compliant solely because E. coli is absent B Bacteriological compliance is one essential requirement, but applicable physical and chemical drinking-water requirements must also be satisfied C Chemical compliance eliminates the need for microbiological examination D Bacteriological and chemical parameters are the same measurements

Question 26 ప్రశ్న 26

Which response is most appropriate when E. coli is confirmed in a drinking-water distribution sample?

A Ignore the result unless consumer complaints are received B Treat it as evidence requiring prompt verification, sanitary investigation and corrective action because the non-detection requirement has failed C Average the result with chemical-test values D Wait until E. coli exceeds 100 CFU/100 mL before acting

Question 27 ప్రశ్న 27

Consider the following statements about bacteriological drinking-water quality: I. E. coli is a specific indicator of faecal contamination. II. Total coliforms are a broader indicator group and can signal treatment or distribution-system integrity problems. III. Current drinking-water requirements use non-detection in a 100 mL sample for the relevant coliform criteria rather than accepting an obsolete routine count. IV. Absence of indicator bacteria in one sample cannot prove absolute absence of every possible waterborne pathogen from the entire system. Which option is correct?

A I and II only B I, II and III only C II, III and IV only D I, II, III and IV

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