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Here we explain how to interpret and thus act on the results of water tests for various types of water contamination. This series of articles explains many common water contamination tests for bacteria and other contaminants in water samples. We describe what to do about contaminated water, listing common corrective measures when water test results are unsatisfactory. We include water testing and water correction measures warnings for home owners and especially for home buyers when certain conditions are encountered, with advice about what to do when these circumstances are encountered. Various treatment methods for contaminated water are reviewed and the pros and cons of each are discussed.

© 2009 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

Emergency drinking water needed? Basic water purification procedures that can be used in an emergency such as after a hurricane, flood, or earthquake are described at   DRINKING WATER - EMERGENCY PURIFICATION and emergency sources of drinking water are described at  DRINKING WATER - EMERGENCY SOURCES.

If community or private wells are back in operating and providing water, do not assume that the water is sanitary and ok to drink until responsible authorities have said so. Even then, local water pipes in a building may be unsanitary and additional cleaning or disinfection may be needed. See WELL CHLORINATION SHOCKING PROCEDURE and See WATER TESTS, CONTAMINANTS, TREATMENT for advice on using a private well for drinking water.

Common Water Contamination Tests for Bacteria Levels - Identifying Unsanitary Drinking Water

This document combines information from various sources including from the Dutchess County NY health department, from Smith Laboratory in Hyde Park NY (914-229-6536), water test developer/suppliers, and other independent sources. Pending review corrections by these sources, the author is responsible for the content which includes opinion and advice based on more than 30 years experience in the field. Because water quality can have major effect on personal health, home owners and home buyers, & ASHI home inspectors should consult with their local health department before performing tests or taking corrective actions regarding water quality.

PA - Coliform Bacteria Test for Contamination in Water: Presence/Absence Test

This standard water test required by many banks, involves pouring use of a chemical Defined Substrate Technology (DST) reagent which produces a color change (or another signal, i.e. fluorescence), both indicating and confirming the presence of total coliform and E. Coli in a sample of drinking water. The test indicates either the presence or absence of this bacteria.

This test, used by most water test companies for real estate transactions does not produce a bacteria colony count. We order this procedure, or the lab will elect this procedure when the water sample is turbid (contains sediment or other material which precludes alternative test procedures). The test is sensitive and specific for the detection of total coliform and E. coli at 1 CFU/100mL of sample in water samples with as many as 20,000 heterotrophic bacteria present per ml. This means that this test for coliform bacteria is not obscured by the presence of other bacteria in the water.

P/A Test results: if the test did not find an indication of a coliform bacteria problem the result will say "Less than 1" or if the lab reports carelessly, "Zero". Accurate lab test reporting would be to say "below the limits of detection" of a given test, and then to specify the limits of detection used. The acceptable level of bacteria in water varies by jurisdiction. For example in some Canadian provinces a higher level of 10 CFU/100mL is permitted. These very slightly higher numbers are allowed because the opinion of health experts is that there is no measurable risk at those levels.

See TOTAL COLIFORM TESTING for details about coliform bacteria test procedures and standards.

See WATER TEST CHOICES & WATER TEST FEES for choices of water tests and our advice about choosing among them.

M.F.T. - Coliform Bacteria Test for Contamination in Water: Membrane Filter Technique

This standard water "test" required by many banks, involves pouring 100 ml of water through a membrane filter. The bacteria present in the water are trapped on the surface of the filter. After an incubation period of 24 hours the coliform colonies present are counted. The count may not exceed 0 per 100 ml according to recently updated New York State Drinking Water Regulations. (MFT=Multiple tube Fermentation Test.)

MFT Test results: If the lab finds apparent unacceptable results with this general test for the presence of any bacteria, the revised NY State procedure requires the lab to measure for E-coli, by performing the MPN procedure as follow up. This is because the presence of non-coliform bacteria present in the water can obscure the test and prevent counting E-coli. The NY State Sanitary Code has no standard for total bacteria count in water supply. The need to go to an MPN test often explains additional delay of up to a week beyond usual time for obtaining water test results.

MPN - Coliform Bacteria Test for Contamination in Water: MPN testing

This test is used when the water cannot be filtered due to turbidity, high iron, large amounts of sediment, or high non-coliform bacteria count. This test involves incubation of measured volumes of sample in liquid nutrients which favor the growth of any coliform bacteria present. This is a statistical method of testing based on the number of positive tubes of media after 48 hours of incubation and 48 additional hours of confirmation.

MPN Test results: As of modified NY State procedures starting in 1991 a count of 0 indicates no coliform and water of satisfactory quality. (MPN=MilliPore Nutrient test.)

See WATER TEST CHOICES & WATER TEST FEES for choices of water tests and our advice about choosing among them.

Interpreting Other Water Test Results

Examples of allowable limits (subject to change) for other tests are listed at Drinking Water Contaminant Levels - New York State Maximum Allowed

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WATER TEST INTERPRETATION
Common Water Tests for Bacteria
  PA - Coliform Bacteria Test
  M.F.T. - Coliform Bacteria Test
  MPN - Coliform Bacteria Test
  Interpreting Other Water Test Results
FAILED WATER TESTS - WHAT TO DO
  Water Test Procedure Errors
  Detecting Water Test Cheating
  Interpreting the Level of Bacteria
  WELL CHLORINATION SHOCKING PROCEDURE
FAILED WATER TESTS - WHEN to RE-TEST
  Wells that Pass a Second Water Test
  Wells that Fail a Second Water Test
  When to re-test a well
ODORS in WATER - TYPES, CAUSES
WATER TREATMENT EQUIPMENT CHOICES
  FILTERS for WATER
  FILTERS - SEDIMENT & IRON
  FILTERS - SULPHUR ODOR
  CHLORINATORS & CHARCOAL FILTERS
  REVERSE OSMOSIS WATER TREATMENT
  REVERSE OSMOSIS CONCENTRATE DISPOSAL
  UV -ULTRAVIOLET LIGHT TREATMENT
  WATER SOFTENERS
  WATER TREATMENT CHEMICAL SAFETY
EPA GUIDE to WATER QUALITY
FHA WATER TESTS REQUIRED
LEAD in WATER, ACTION GUIDE
ODORS IN WATER
SEWAGE CONTAMINATION
WATER CONTAMINANT LEVELS
WATER TEST INTERPRETATION
WATER TESTING GUIDE
WATER TREATMENT EQUIPMENT CHOICES
WATER ODORS, CAUSE CURE
WATER PUMPS & WELLS
WATER QUALITY TESTS, CONTAMINANTS, TREATMENT
WATER QUANTITY IMPROVEMENT
WATER QUANTITY USAGE GUIDE
WATER SOFTENERS
WELL SHOCKING GUIDE
WELLS CISTERNS & SPRINGS
WELL CHLORINATION SHOCKING PROCEDURE
  Chlorine in Wells - Safety Warnings
  Well Chlorination Procedure Details

More Information on Building Diagnostic Inspections and Repairs

• Cheating on water tests: Testing Water for Real Estate Transactions - make sure your water test is valid
• Drinking Water Testing Advice for home buyers home owners home inspectors
• Interpreting Drinking Water Test Results and Correcting Unsatisfactory Water
• Drinking Water Contaminant Levels - Maximum Allowed
• Drinking Water Contamination and Pollution How to Detect, Test, Correct, and Prevent Well Water Contamination - US EPA - Groundwater
• Lead Contamination in Drinking Water: Testing & Correction - Advice (This Article)
• Lead Testing & Correcting Contamination from Lead Water Supply Lines/Entry Mains - Lead Pipe Problems/Advice
• Extreme Lead Poisoning Symptoms Suggested by Feb. 2006 NY Times Article on Kosovo Roma Camps
• ATSDR: Nitrate/Nitrite Toxicity [Big, Slow-Loading File] U.S. Government ATSDR Science Corner - 2.5MB PDF
• Water testing for Pesticides: comprehensive and pesticides-example parameters
• Water Testing: background comments on classes of water contaminants, & links to home buyer advice about water testing, drinking water, water supply
• When and How to Shock or Chlorinate a Well - Procedure for Shocking a Well to (temporarily or maybe longer) "Correct" Bacterial Contamination
• Water Requirements, Home & Outdoor Living
• Typical Water Tests & Fees this water test fee schedule applies when testing is combined with other onsite building inspection services
• Drinking Water testing, contamination, correction - all topics
• General water testing and corrective measure advice: contact your local health department.

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