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Interpreting Drinking Water Test Results, Correcting Unsatisfactory Drinking Water, Choices of Water Treatment Methods for Contaminated Drinking Water WaterAPedia © Enter your search terms Submit search form   Search This Website - InspectAPedia.com

This website 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. © 2008 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use the links at page left to navigate this document or to go to Other Website Topics. Green links at left show where you are in our document & website.

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.

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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.)

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

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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

What to Do About Failed Water Tests - How to Correct Unsatisfactory or Contaminated Drinking Water

Water Test Procedure Errors: Assure Proper Water Sample Testing Procedures Were Followed, Detecting Water Test Cheating

If a result is not satisfactory the following questions must be addressed:

• Was the sample properly taken?
• Water Sample Collection Procedure: (We remove the faucet, aerator which can harbor bacteria, run at least 20 minutes of water, 24 hours if house is unoccupied, and fill the container without touching its interior.)
• Did someone tamper with the water supply? See Cheating on water tests: Testing Water for Real Estate Transactions - make sure your water test is valid
• Has work been done on the water system that was not followed by an adequate disinfection when the work was completed? (New pump or pipes installed recently?)
• Is it a new well that has not been in daily use
• Was the well improperly disinfected? with inadequate concentration, contact time, or time between treatment and follow-up testing?
• Has the house been vacant and the water system not in use for an extended period of time
• Is the well properly sealed
• Are there cartridge type or R.O. (reverse osmosis) filters in use on the water system? (These can be a source of bacterial contamination.)
• Was work recently done on the well? Installing a new submersible (in-well) pump and well line or foot valve means pulling the piping out of the well, lying it on the (unsanitary) ground surface, and then replacing in the well. The well should have been disinfected after such work. On occasion I've found a similar problem occurring with indoor plumbing work.
• If the source of the contamination is not due to an ongoing situation, for example bad ground water source, then a disinfection of the water system will solve the problem.
• What was the level of contamination detected? This question is explored next.

Interpreting and Acting On the Significance of the Level of Bacteria Found in a Water Test

I prefer the MFT/MPN test to the P/A test because getting an actual count or "number" of CFU/100ML is diagnostic (as I describe here) whereas a P/A test simply says OK or NOT OK with no indication of the level of contamination present.

For example, consider two wells with a persistent source of bacterial contamination. If a well that fails at 15 CFU/100mL is "shocked" the low starting count means it's easier to cover up the persistent problem source and more time may be needed for the bacteria to reappear. This would affect your follow-up testing strategy.

By contrast, if a second well with a persistent source of bacterial contamination fails at >10,000 CFU/ml, first it is very unlikely that any "well shock" treatment will be effective, and second, the level of contamination is so great that if a seller came up with a subsequent "pass" on a bacteria test without installing purification equipment or without telling me what problem was found and fixed, I would be very skeptical about the reliability of the follow-up test.

So while a property seller/owner may prefer to "shock" a well and re-test, that procedure, used alone, might or might not be acceptable. What to do after a seller/owner has "done something" to the water supply and re-testing has been done is discussed below.

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When and How to Shock or Chlorinate a Well - Procedure for Shocking a Well to (temporarily or maybe longer) "Correct" Bacterial Contamination

This is a general description of a common procedure used to sterilize well water and water equipment. This information is from the Dutchess County Health Department's environmental laboratory. The purpose of shock disinfection of a well system is to destroy bacterial contamination present in the well system at the time of disinfection and is not intended to kill bacteria that might be introduced at a later time. Therefore it is vital that the well be constructed so that no new contamination may enter the well following completion of the shock disinfection. In order to achieve a satisfactory disinfection of the system, the bacteria must be brought in contact with a chlorine solution of sufficient strength and remain in contact with that solution for a sufficient time to achieve a complete kill of all bacteria and other microorganisms.

Chlorine in Wells - Safety Warnings

When working with chlorine, people should be in a well-ventilated place. The powder or strong liquid should not come in contact with skin or clothing. Solutions are best handled in wood or crockery containers because metals are corroded by strong chlorine solutions.

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Details of the Well Chlorination Procedure - Exactly How to Shock a Well, Where to Put Chlorine, How Much Chlorine to Use to Shock the Well

If drinking water has been tested and has not passed standards for safe drinking, or any time the building water supply system has been opened for repairs, the well should be disinfected following these procedures, and should be re-tested as described herein.

• Pour Clorox or hypochlorite granules down into the well. Some people use swimming pool chlorine tablets which have the advantage that they sink to and sterilize water at the well bottom, and the disadvantage that it takes longer to flush out the chlorine.
• Health department officials can give more precise guidance about the amount of disinfectant needed based on the depth of the well. Common guidelines:
• Well depth 100' - 3 cups Clorox or 2 oz. of granules.
• Well depth 200' - 6 cups Clorox or 4 oz. of granules.
• Well depth 300' - 9 cups Clorox or 6 oz. of granules.
• Well depth 400' - 12 cups Clorox or 9 oz. of granules.
• Well depth 500' - 1 gallon Clorox or 12 oz. of granules.
• NOTE to be accurate in reaching the necessary concentration of chlorine in your well, treat the "depths" listed above as if they were the height of the actual column of water in your well (assuming a standard casing which is 1.5 gallons per foot of height). So if your well is 400 feet deep, but if 100 feet of it is air, your water depth is actually 300 ft.
• Introduce the chlorine solution into the top of the well. Remove the cap at the upper terminal of the well casing and pour the chlorine solution down the inside of the casing. If the well casing terminates through the floor of a pump house, then the casing is required to have a well seal at the upper terminal [i.e. at the top of the casing]. This well seal can be loosened and the chlorine solution introduced into the well at that point. In a large diameter well [such as a public supply company's well], the chlorine solution should be poured or splashed around the wall of the well so that all inside surfaces of the well are brought into contact with the strong chlorine solution.
• Using a garden hose, spray water down into the well pipe to wash the chlorine solution down to the bottom of the well. Ten gallons of water should be enough. [More won't hurt nor risk running the well dry since you're recycling the well water through the plumbing and back to the well.]
• Turn on all cold water household taps until you can smell the Clorox coming out of the faucet farthest from the well.
• Turn off the water and do not use it for 8 to 24 hours. Seal the top of the well. Do not run laundry with this chlorinated water or it may bleach clothing unexpectedly.
• At the end of the standing period, operate the pump (run the water) water until you can no longer smell the Clorox. Do not run Clorox into the septic system - run water outside through an outside faucet or hose. There should be a hose connection at the at the bottom of the water tank. When you no longer smell chlorine at the hose draining the water tank, close off the drain and open all faucets in the house to flush out house piping for fifteen minutes or until you no longer smell or taste chlorine [whichever is longer].
• Retest the water after all the Clorox or chlorine is out of the system and the water has been used for 5-7 days (typical health department guideline) or 7-10 days (my suggestion) after the disinfection. The longer you wait until the retest the more valid will be the results. I elaborate on this point at "When to re-test" below.

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Acting on Unsatisfactory or Contaminated Water Test Results - Advice for Home Buyers & Home Owners

Handling Failed Wells that Pass a Second Water Test: What to do if water passes after disinfection

• If the contamination was a relatively low bacteria count and was caused by an unsanitary growth in plumbing equipment this treatment can "correct" the problem.
• If the contamination was a relatively low to modest count and is caused by a persistent source of contamination, this treatment can appear to correct the problem by killing off bacteria. But the problem can recur.
• If the contamination is from a major source, with a high bacteria count, repeated sterilization and testing of the well may yield inconsistent results, sometimes passing, sometimes not.
• "Shocking" a well can temporarily make unacceptable water look fine. If no other corrective measures were taken than to "shock" the well, it is appropriate to follow the first acceptable water test with a second and perhaps even a third, spaced a week or more apart.
• If in a real estate sale transaction the schedule does not permit these tests before closing, a buyer should consider requiring an escrow fund set aside during purchase of the property. This fund will guarantee acceptable water while giving the buyer a reasonable time, perhaps a month, to perform additional testing.

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When to re-test a well that has been shocked with chlorine bleach or some other disinfectant

To be maximally effective at attempting to disinfect a well, the chlorine solution needs to be in contact with the entire well casing and piping and water storage tank for 24 hours. Then the bleach-treated water is flushed from every fixture until there is no more bleach odor. A realtor/seller anxious to "pass" a bacteria test will try for an immediate re-test at that point.

WARNING: Wait. Don't re-test a well too soon. I suggest a minimum of five days, preferably seven to ten days before re-testing a shocked well. If there is a persistent source of bacterial contamination shocking the well won't fix anything. The longer you wait the more time you're giving for the bacteria to reappear at a level sufficient to be picked up in the next water test. If circumstances force a too-quick follow-up bacteria test real to meet a estate closing date before adequate wait time has been allowed for re-testing to be more credible, I recommend that the parties agree to escrow the cost of a proper water treatment system ($5000. to $10,000) and to allow the new buyer 30 days to conduct follow-up testing. If at the end of that period the well is ok the escrow can be released.

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Handling Failed Wells that Fail a Second Water Test Again: What to do if water fails a follow-up water test after well disinfection by Chlorination or Well Shocking

• If the test still is not satisfactory, it is likely that there is a persistent source of contamination. Common sources of contamination include loose or damaged cap on buried well casings, loose or damaged pitless adapter (where buried water line enters the well casing), a bad plumbing connection in piping between the well and the building, spiders living in the well head and possibly insects they've dropped into the well, a dead animal in a well which was not properly capped, and, less common, a cracked or damaged well casing. Damaged well casings can involve significant expense to repair or replace.
• Since water systems can change, drinking water from private wells should be analyzed on a regular basis. The frequency of testing should be determined by the history of the water quality of the well.
• Usually the property owner/seller is responsible for correcting unacceptable water. Check with your attorney and your contract regarding this matter.
• Often sellers have the well "shocked" using the sterilization treatment described above.
• In addition to sterilizing the well, an owner/seller might:
• Find the contamination source: have an experienced plumber or well service company look for, find, and correct a source of contamination such as a bad plumbing connection at the well (pitless adapter or well casing cap), bad plumbing between well and house (broken or leaky pipe joint), or bad or soiled plumbing components inside the house.
• install water treatment/sterilization equipment such as a chlorinator/charcoal filter system or an ultra-violet light system. These systems work but require maintenance. Water treatment equipment are discussed in the next section.
• Correcting the source of contamination is naturally preferred. But if a home is being sold, often schedule pressures do not permit longer investigation by a plumber to find a problem if it is not obvious. Therefore to provide safe potable (drinkable) water immediately, a water purification treatment system may be installed. If that course of action is followed, we still recommend that the new owner/occupants attempt to find and correct the source rather than having to maintain equipment.

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Water Treatment for Contamination, Hardness, Odors, Sediment, Etc: choices of systems, recommendations

While I distinguish between having to treat water because it is not potable, and wanting to treat drinking water because of an aesthetic concern like odor, taste, smell, or staining, it is often the case that the equipment used for one purpose can also address the second set of concerns.

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

When is it reasonable, desirable, or actually necessary to install water treatment equipment:

• time does not permit thorough diagnosis and determination of the source of water contaminants (you have to move in and drink the water, or the bank won't issue the mortgage for a property purchase)
• water potability appears to be unreliable: a bacteria problem may have been temporarily masked or "corrected" by "shocking" the well in the past but follow-up testing suggests that it returns, perhaps seasonally as water tables change. See "When and How to Shock or Chlorinate a Well - Procedure for Shocking a Well to (temporarily or maybe longer) "Correct" Bacterial Contamination".
• There is a persistent source of water contamination - a potability or health issue
• There is a persistent source of an aesthetic water problem: hard water, sulphur odors (rotten eggs), iron, or other such contaminants.
• When people in a residence are at unusual health vulnerability: immune impaired, elderly, sick.

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Pros/Cons: Advantages and Problems with Various Types of Water Treatment Equipment for Bacterial or Bacteriological Contamination

• Water Filters as Purifiers
• UV - Ultraviolet light as a Water Purifier
• Reverse Osmosis Systems for Water Purification
• Chlorinators with Charcoal Filters for Water Purification
• Aesthetic water contaminants and treatment systems: sediment, iron, odors, taste
• Water Softeners
• Sediment filters and Iron filters
• Sulphur odor filters or Sulphur Treatment Systems
• Water Treatment Chemical Safety Warnings

Water Filters as Purifiers

I suspect any mechanical or charcoal filter is either unreliable or short-lived. OPINION: For pathogens or bacteria this is a poor choice of water treatment.

UV - Ultraviolet light as a Water Purifier

UV systems use a tube containing a ultraviolet light, installed at the water pressure tank so that water entering the system is exposed to this sterilizing process. The "UV" can kill bacteria in water, provided that the flow rate of water through the device is not too fast (needs exposure time) and provided that the water is not too obstructed with sediment and provided that the light source is cleaned - the bulb needs to be changed periodically.

OPINION: I'm uncertain how one knows that such a system is working reliably without periodic testing and bulb replacement. Worse, such systems do nothing to actually remove other pathogens and less than nothing to remove chemical contaminants, odors, sediment, or other problems that may be present. This treatment method is a last choice for reliability and comprehensiveness of water treatment.

WARNING: Property sellers often install this least-expensive "solution" in the course of a real estate transaction in order to meet the minimum requirements of a buyer's lender to provide "potable water." However since a lender (bank) often requires only a bacteria test as a measure of water potability, and since often only that narrow test is performed, the new owner/residents may have no idea whether or not there are chemical or other contaminants in the water supply.

Since one of the most common ways that bacteria enters a well is through a defect at the pitless adapter (joining the water pipe to the well casing) or at a buried well cap that is leaky or open. In such cases the presence of bacteria in water is really an indicator of ground water leakage into the well. This means that anything that is on the ground or in the soil around the well is likely to be entering the water supply. So treating for bacteria may be failing to address other contaminants. Further testing for other contaminants would be appropriate if a well fails a bacteria test.

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Reverse Osmosis Systems for Water Purification

Reverse osmosis (RO) systems take advantage of the ability of water molecules to pass through a filter membrane which at the same time keeps out many other (non-dissolved non-chemical) contaminants.

OPINION: this method works well for some contaminants, as a point-of-use system. RO wastes quite a bit of water and does not address some chemical contaminants.

Chlorinators with Charcoal Filters for Water Purification

A typical very effective treatment system for water contaminated by a persistent source bacterial contamination involves the injection of chlorine into the water supply, a holding tank to permit sufficient exposure time and concentration for the chlorine to do its work, and a post-processing charcoal filter to remove the chlorine from the water as it leaves the system. These systems will also remove modest levels of sulphur and other odors. If the water has a high level of sediment, pre-filtering may be necessary to avoid clogging the charcoal with debris. There is an operating cost as the charcoal filters need to be changed periodically.

OPINION: A water treatment specialist will often test your water at no charge in order to develop a profile of the contaminants or aesthetic contaminants in water and thus to recommend a specific water treatment system.This "free water test" service is a great deal for building owners and buyers so long as they realize that the water treatment company wants to sell water treatment equipment. Only a very foolish water treatment company would be dishonest about what's in the water, but some companies may be reluctant to outline all of the treatment alternatives. If you're in doubt have some independent water tests done before spending on a costly system. If I had to live with bacteria in my water supply, this would be my treatment system of choice.

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Aesthetic water contaminants and treatment systems: sediment, iron, odors, taste

Water Softeners

Water softeners remove minerals (mostly calcium and magnesium) from a "hard" water supply. If your water is hard (measured in "grains of hardness") you want a water softener installed not only for aesthetic reasons (like getting a good lather when shampooing your hair) but also to avoid clogging the water supply piping with minerals (especially the hot water and very especially where tankless coils are used to provide hot water). Most water softeners work by an ion-exchange process: swapping a small amount of salt or sodium into the water to cause calcium and manganese to precipitate out as dirty sludge (which is periodically removed by backwashing the treatment system). If building occupants require a zero level of sodium in drinking water they may want to install a reverse osmosis point of use supply treatment or in some homes people simply run a water supply line from ahead of the water softener to a single faucet to be used for drinking water.

More Information on Water Testing, Water Contamination, & 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.

Building & Environmental Inspection, Testing, Diagnosis, Repair, & Problem Prevention Research & Advice

The Mold Information Center: What to Do About Mold in Buildings, When and How to Inspect for Mold, Clean Up Mold, or Avoid Mold Problems

Home Inspection Construction Consulting Services & advice for home buyers

Use this simple, economical mold test kit by following our instructions on how to collect and mail mold samples to our lab

Environmental Inspection, Testing, & Diagnosis On-Site IAQ, Gas, Air Testing, Mold Investigation, Sick Building Diagnosis, Lab Services, & Remediation Plan Preparation - indoor air quality testing, problem source determination, supporting lab work, written remediation plan addressing removal of environmental and other hazards and prevention of their recurrence.

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