Photograph of a total <EM>Coliform</EM> test with <EM>Coliform</EM> present - liquid turns yellow Guide to Water Contaminants & Water Tests
Index to Articles on Water Contamination Limits, Water Testing Advice & Procedures

  • POST a QUESTION or READ FAQs about when, how, and why to test well water for contamination: advice for property or home buyers and property or home owners who use a private well for drinking water

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This article gives advice on water testing for property or home buyers or home owners, with focus on a strategy for assuring the quality of well water by site inspection, property history investigation, and strategically-selected water tests for contamination.

Discussed here: Water potability testing guide - water bacteria test guide. Articles Describing Types of Water Potability Tests, Water Purity Tests, Test for Other Water Contaminants. How to conduct water tests, what water tests to order, how to avoid dishonest or cheating on water tests.

The articles listed on this water testing advice page will answer most questions about drinking water testing, focused on testing water supplied from wells, & water tanks as well as many other building plumbing system inspection or defect topics.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Water Testing Advice

Dripping water at a faucet (C) Daniel FriedmanHow to Investigate for Water Contaminants at a New or Unknown Property or a Private Drinking Water Well

General advice on water testing when buying a rural property:

The minimum test for water potability elected by many property owners or buyers looks only at bacteria. Some government lenders require more extensive tests such as the FHA and Title-5 water potability testing series.

Those and similar "water test package" deals offered by water testing labs can be a good way to spend your water testing dollars as they test for the most common contaminants found in well water in many areas.

This article is a companion to WATER QUALITY TEST CHOICES & WATER TEST FEES - how to decide just which water tests to order.

Watch out for "False Negative" assurances that Well Water is "Pure"

First of all, no water test assures against all possible contaminants in water.

Second, water tests that focus on water potability (is the water safe to drink) may miss other important water conditions, such as water that is too high in mineral content, clogging pipes and water heaters (see MEASURE WATER HARDNESS), or water that is too acidic or corrosive, causing leaks in copper piping (see CORROSIVITY or ACIDITY of WATER).

Watch out: even so, property buyers should beware of ordering water tests arbitrarily, Because of the enormous number of potential chemical contaminants that might show up in water, there is a risk of accepting a "false negative" result, that is, a risk of assuming that there are no contaminants in drinking water after a specific water contaminant tests shows a negative result.

It may simply be the case that a contaminant that is present was not detected because it was not within the scope of the tests performed.

Therefore to be more confident about the quality of water at a property whose water and land history may be unknown, we recommend a series of escalating steps in water testing and other investigative measures.

At several points in the investigation process a property buyer or new owner may decide that the information obtained so far provides enough confidence, or that the information suggests that additional levels of water testing are appropriate.

Site investigation for well water quality concerns

This important step in investigating well water quality includes

A visual inspection for things that might raise a red flag: evidence of chemical, fuel, or fertilizer storage on the property or nearby at sites that drain onto the property, nearby industry (industrial chemicals), nearby orchards (pesticides) or farms (fertilizers) whose land drained across or onto the property.

Among the most basic observations will be the location of the well and its proximity to septic system drainfields, barns, livestock pens, or farm chemical storage tanks or fuel tanks. And of course the type of well (dug, driven point, steel well casing) and depth also have implications for the probability of contamination by surface runoff or subsurface contaminants.

Investigation by asking neighbors, the local health department, and nearby water testing laboratories to determine if they know of specific water quality problems that have been discovered in the neighborhood. This step can sometimes provide surprising payoff such as questions by one of our clients whose Pawling NY well had tested as "OK" for several contaminants.

A neighbor pointed out that a paper company had for years dumped acetone and other waste chemicals in an empty field across the street from the client's well. Testing found unusual levels of acetone in the water - an uncommon contaminant as acetone is so volatile, and not something that anyone would have tested for without a clue from a helpful neighbor.

Professional investigation services are available from environmental inspection and testing firms who will research government data bases of known sources of water contamination, but watch out: such investigations may not disclose small local industries or contamination sources.

Some Community Drinking Water Wells May Also Be Contaminated

In the U.S. and most other countries community water supplies, often defined as serving 25 or more homes, must be tested and found to comply with national or federal drinking water standards.

In the U.S. "The Safe Drinking Water Act (SDWA) is the federal law that protects public drinking water supplies throughout the nation. Under the SDWA, EPA sets standards for drinking water quality and with its partners implements various technical and financial programs to ensure drinking water safety. " - original source: retrieved 2018/02/13

However recent studies reported both in professional journals and in the national press point out that local water companies frequently fail to meet federal safe drinking water standards.

Contaminants in community or municipal water supplies can vary from the infamous lead contamination of water supply in areas of Flint Michigan to other contaminants such as nitrates, arsenic, or pathogens. There may also be municipal drinking water contminants that are themselves a byproduct of the disinfection process used by the municipal water treatment facility.

In a new study published in the Proceedings of the National Academy of Sciences, researchers found that, since 1982, between 3 and 10 percent of the country’s water systems have been in violation of federal Safe Drinking Water Act health standards each year.

In 2015 alone, as many as 21 million Americans may have been exposed to unsafe drinking water. - Plumer, Brad, Nadja Popovich, " Here Are the Places That Struggle to Meet the Rules on Safe Drinking Water", The New York Times, 2018/02/12 original source: retrieved 2018/02/13, with more citations at REFERENCES.

Choosing Specific Water Test Lab Tests for Water Quality

Informed by step 1 above, the minimum water test that is performed is a bacteria test or "water potability test".

While the minimal "presence/absence" test is popular and inexpensive, the test gives a "go / no-go" result (there is or is not a coliform bacteria level at or above 1 colony forming unit (CFU) per 100 ml of water).

Keep in mind that no water test assures a zero level of bacteria in water nor do health regulations require it. A more costly water test for bacteria provides an actual count of the bacteria level found, if above certain thresholds - this is a much more useful test as it is diagnostic both before and after attempts to correct a bacteria problem.

Bacteria testing does not itself assure anything about the presence or absence of chemical contaminants or aesthetic contaminants (silt, odors, hardness) in well water.

But nevertheless, if a water test "fails" a bacteria test, because a common source of high bacterial levels in well water is the leakage of surface runoff into a well, that means that there is also a higher risk of the presence of other contaminants that might be found on the ground surface (pesticides, fertilizers).

Therefore even if a home owner/buyer decides to perform only the most minimal bacterial testing, the result can be a red flag that more thorough testing for other contaminants is in order.

Where a well is on or near farmland or orchards, water testing labs will often recommend one of two pesticide tests (depending on property age and whether or not it's appropriate to test for DDT or chlordane or newer pesticides, as well as tests that can detect common ingredients in fertilizers.

At a property in Dutchess County, NY, where we found a "permanently-parked" trailer that had been used by Terminix™ to store pesticides I was worried about possible storage leaks and thus pesticide contamination in the nearby well.

Tests for pesticides found that there was no contamination of the well nor of soil around the trailer. The pest control company had been careful.

But a subsequent investigation of the property's history disclosed that a metal plating shop had been present in one of the buildings on the site.

Tests found high levels of chromium contamination of soils, water, and even a nearby stream bed, resulting in a serious environmental contamination issue that involved the new property owner as well as local, state, and federal environmental officials.

Where the visual inspection or a study of the property history discovers specific potential sources of contamination, it makes sense to discuss these with the water test lab director to decide what tests are most useful to perform.

Watch out: this discussion has focused on well water quality - what is "in" the well water that may make it unsafe or unpalatable to drink. We also mention and refer readers to other important water conditions, such as water that is too high in mineral content, clogging pipes and water heaters

(see MEASURE WATER HARDNESS), or water that is too acidic or corrosive, causing leaks in copper piping

(see CORROSIVITY or ACIDITY of WATER). An equally important question is "does the well provide enough water" - a topic discussed



Water Contaminants, Water Tests & Test Parameters, Water Treatments

Best bet for getting help with water contaminationor water tests, treatments, cures: use the search box found near the top or bottom of any InspectApedia article.

Standards for Coliform in Drinking Water

Question: is our water safe to drink if coliform is detected?

2018/10/16 Pradeep said:

I have tested our drinking well water. In it the total Coliforms MPN/ 100 ml is 1600, Thermotolerant coliforms MP N/ 100 ml is 175, and Escherichia coli MP N/ 100 ml is less than 2.

Is the water good for drinking and how can we get the waterpurified?

Reply: no.

No Pradeep, by US standards and those used in some other countries,

The Maximum Acceptable Concentration of both Total Coliforms and E-Coli for Drinking Water is ** none detectable per 100 mL **

This means that for every 100 mL of drinking water tested, NO total coliforms and NO E.coli should be detected.

While total coliform is common in groundwater and is not necessarily harmful itself, when it is found in drinking water it should be understood to be an indicator that unsanitary water is entering the water supply.

When E-coli (Echeria coliform) is present in drinking water it is harmful, containing pathogens that can cause serious illness.

For details about bacteria testing in the water supply you may want to read BACTERIA TEST GUIDE - tests the level of microbial ccontaminants in water.

Examples of Coliform Standards for Drinking Water

Canadian Standards for Coliform Levels in Drinking Water

The Canadian Drinking Water Quality Guideline for total coliforms is none detectable per 100 mL.

The Canadian Drinking Water Quality Guideline for Escherichia coli (E.coli) is none detectable per 100 mL.

Maximum Acceptable Concentration for Drinking Water = none detectable per 100 mL

Mexico Sanitation & Water Quality Standards

According to the Mexican constitution responsibility for water supply and sanitation services delivery rests with 2,517 municipalities since the decentralization of 1983. (Pablos 2002)


UK United Kingdom Drinking Water Standards including for Coliform

United States Standards for Coliform in Drinking Water


For E. coli (EC), the Maximum Contaminant Level Goal (MCLG) is set at zero.

Total coliforms are a group of related bacteria that are (with few exceptions) not harmful to humans. A variety of bacteria, parasites, and viruses, known as pathogens, can potentially cause health problems if humans ingest them.

EPA considers total coliforms a useful indicator of other pathogens for drinking water.

Total coliforms are used to determine the adequacy of water treatment and the integrity of the distribution system.

Watch out: people with weakened immune systems may be more vulnerable to pathogens or other contaminants in drinking water. Treatments that kill coliform bacteria are generally not effective against other pathogens that may be present. See:

WHO World Health Organization Drinking Water Guidelines & Coliform Standards

What to Do About Coliform in Drinking Water

If coliform is the only contaminant in drinking water AND after establishing that you can't correct the problem by shocking the well and fixing surface water leaks into the well then you will want to install a water disinfection system.

Watch out: before installing any water treatment system for bacteria you should have more-extensive water testing done to find out if there are other non-bacterial contaminants that also need to be removed.

That's because the presence of coliform in drinking water often means that surface water is leaking into the water supply.

When surface runoff leaks into a drinking water supply, any contaminants present on the surface, including for example pesticides or agricultural chemicals, are likely to be in the water and also are likely to be at levels meriting removal.


Continue reading at WATER QUALITY TEST CHOICES & WATER TEST FEES - how to decide what to test for in your water supply, or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see BUILDING CODE DOWNLOADS - free downloadable PDF files of building codes & standards









Or see WATER TEST RESULT INTERPRETATION - what the results mean and what to do about them

Watch out: also see WATER TESTING ADVICE for home buyers and building owners: water contaminants, water test procedures, well shock procedures, preventing drinking water contamination,

and CHEATING ON WATER TESTS that warns about how people accidentally or on purpose can obtain incorrect water test results.

Or see WATER TREATMENT EQUIPMENT CHOICES - home - options for water disinfection, treatment, purification, or removal of other un-wanted substances

Suggested citation for this web page

WATER TESTS for CONTAMINANTS at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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