FAQ / Bacteriology FAQ / questions and answersFAQ / Bacteriology FAQ / questions and answers

Bacteriology FAQ

Effective September 1, 1992, the U.S. Environmental Protection Agency and the California Department of Health Services adopted a set of drinking water standards known as the Total Coliform Rule. Drinking waters with one or more coliform bacteria per 100 mL are now considered a potential health risk. North Coast Labs offers two tests for coliform bacteria in potable waters: the Presence/Absence Test and the Quanti-Tray/2000 Test. These analytical methods use the EPA-approved reagent MMO-MUG, a minimal media that produces complete results within 28 hours of inoculation. These tests provide the client with total coliform and E. coli results.

Important Things To Remember

  1. The minimum sample volume of a potable water sample is 100 mL (note the 100 mL fill line on the sample bottle.)  
  2. The analysis of potable (drinking) water samples must be started by the lab within 30 hours of sampling. The analysis of source water samples must be started within eight hours of sampling.
  3. Bacteriological water samples will be accepted Monday through Thursday between 8:30am and 5:00pm and Friday between 8:30am and 12:00 noon.
  4. Samples for regulated systems must must be iced during transport. Samples are to be kept at less than 10ºC from the time of collection until they are delivered to the laboratory. This can be as simple as placing the sample container is a zip lock bag with ice.
 

Questions

Commonly asked questions and answers are provided below. The answers are meant as quidelines only and do not take into account many extenuating circumstances. We suggest you contact your local health department or your physician about more specific health risks of your water supply.

What are Coliform bacteria? Are they harmful?
Why test for Coliform bacteria in drinking water?
Which bacteriological test should I choose?
There is some powder in my sample bottle. Should I rinse this out before I take the sample?
Can I sterilize my own container to take a water sample?
What is the significance of a positive test result?
What should I do if my water tests positive for Coliforms?
What, besides bacteria, could make my water unsafe to drink?
When should I test?
How do I pay for a bacteria test?
How do I get test results?
How do I disinfect my well?
How do I find the source of Coliform contamination?

 

Answers

What are Coliform bacteria? Are they harmful?

Coliform bacteria are very common in the environment. Many species live in the soil, some in plants or rotting vegetation, while others like E. coli inhabit the intestines of mammals – including humans. Most strains of coliform bacteria are relatively harmless by themselves.

Why test for Coliform bacteria in drinking water?

The coliform group of bacteria is the principal indicator of the sanitary quality of water for domestic, recreational, industrial, and other uses. Since these bacteria do not thrive in water, the presence of coliforms indicates possible contamination and potential health risk. The presence of fecal coliforms like E. coli indicates fecal contamination of the water supply. Fecal contamination of domestic waters can result in the transmission of diseases like dysentery, hepatitis, typhoid and giardiasis.

Which bacteriological test should I choose?

Presence/Absence
Since the presence of one or more coliform bacteria per 100 mL sample is considered unsuitable for consumption, the Presence/Absence coliform test is recommended for most homeowners and water distributors. The Presence/Absence test simply gives results of present or absent for total coliform and E. coli within 28 hours of inoculation.

Quanti-Tray/2000 Test
This test provides a quick determination of the density of total coliform bacteria and E. coli in the water sample. Rather than a result of present or absent, the most probable number (MPN) of bacteria in the bottle is reported. This test is recommended when tracking the source of contamination, comparing the efficacy of water filters or sterilization techniques or monitoring a known contamination source. The Quanti-Tray/2000 test can quantify up to 2419 coliform bacteria per 100 mL of undiluted sample.

3x5 and 4x5 Analyses
The 3x5 test is used to monitor coliform bacteria densities in wastewaters (industrial and municipal effluents) and recreational waters. The 3x5 Multiple Tube Fermentation (MTF) test requires 96 hours. The 4x5 and 5x5 MTF tests are also available for soil samples believed to be highly contaminated with animal or human waste.

Heterotrophic Bacteria
Heterotrophic microbes include bacteria, molds, and yeasts. North Coast Labs offers Heterotrophic Plate Counts, which measure the relative purity of laboratory, potable and source waters. These tests require prior notification by the client.

There is some powder in my sample bottle. Should I rinse this out before I take the sample?

No. This is sodium thiosulfate, a chemical that neutralizes any chlorine that may be in your water. Your test will be more accurate if you leave this in place. For best results, read and follow the sampling instructions carefully.

Can I sterilize my own container to take a water sample?

Not for any "official" test which must have results sent to a public agency or lending institution. We do not recommend it for private use either. Test results may be affected by either incomplete sterilization or residual disinfectant. If you must sterilize your own container, wash it thoroughly and rinse twelve times with the water to be tested and then sterilize in a pressure cooker for 5 minutes at 121 degrees Celsius (250 degrees Fahrenheit).

What is the significance of a positive test result?

According to public health officials, you should not drink water that tests positive for any coliform bacteria. If fecal coliform or E. coli bacteria are present in your drinking water, your risk of contracting a water-borne illness is increased. Fecal-contaminated water should not be consumed by humans, pets or livestock. It is also unsuitable for bathing, washing dishes or watering the garden.

What should I do if my water tests positive for Coliforms?

Operators of public water systems (motel and restaurant proprietors, landlords, mutual water systems, community service districts and municipalities) have extremely specific rules regarding the reporting of positive coliform results and the steps to follow. Contact the appropriate regulator immediately to stay in compliance with the law.

For private homeowners with their own water systems, if you have E. coli you should first stop using the water. Second, you may want to resample and retest your water if you believe the sample may have been accidentally contaminated. If your water is drawn from a well or a spring, you may want to track the source of contamination by sampling at various points in the system, for instance at the wellhead, settling tank, and indoor tap.

If your water supply is unquestionably contaminated, you can either disinfect your water system, locate and "remove" the source of contamination, or invest in a filtration or automatic chlorination system.

One method for disinfecting your water system is called "shock sterilization." Pour one gallon of Clorox bleach in your well or spring and open all your faucets until you can detect the odor of chlorine from each faucet. DO NOT attempt to drink your water at this stage! Allow the bleach to remain in the lines and the pressure (or holding) tank as long as possible (3 to 4 days is good; 1 day may be adequate in some cases.) Open all the faucets once again and run the water until you cannot smell chlorine any longer. Use the water for 7 to 10 days, then retest for bacteria.

NOTE: Chlorination of well water that contains iron and /or manganese will temporarily worsen the dissolved metal problem. It may take up to several weeks for your water to return to normal. If in doubt, put a few drops of bleach into a glass of your water and let it sit overnight. If the water looks like cloudy orange juice the next day, you will have temporary iron problems after a shock treatment. This means that if you install a chlorinator, you will probably need a filter system or settling tank to alleviate the problem.

What, besides bacteria, could make my water unsafe to drink?

We are fortunate on the North Coast that our drinking waters are largely free of industrial pollutants. The most common problem with our groundwater is excessive iron and manganese. They cause orangish to brownish cloudy water and stain anything. An excessive amount of copper and/or lead in tap water is generally related to home plumbing and the corrosivity of your water. Metal analysis of your potable water supply is available at North Coast Labs. Surface waters and springs used as source water for drinking water may harbor Cryptosporidium or Giardia, aquatic protozoans which can cause intestinal illnesses.

When should I test?

The best time to test is during wet weather when coliform contamination is most common. Whether the test result is positive or negative, it only represents a “snapshot” of your well’s water quality. Regular water testing is recommended for consumers who are not serviced by public water providers.

How do I pay for a bacteria test?

Please be prepared to make payment by cash, check, or credit card at the time you bring your water sample to the lab for testing. If you are paying by check or money order, address your check to North Coast Labs. If you wish to pay by credit card, Mastercard or VISA only, complete the information at the bottom of the information/test form provided for this purpose.

How do I get test results?

You will be notified by North Coast Labs if your drinking water sample has any positive results. Results will be mailed to the address on your form after the completion of the test.

How do I disinfect my well?

The following document outlines guidance to disinfect your well or water system:

Procedure for Disinfecting Wells and Water SystemsProcedure for Disinfecting Wells and Water Systems

How do I find the source of Coliform contamination?

The Humboldt County Division of Environmental Health has published the following troubleshooting checklist for detecting sources of coliform contamination:

Troubleshooting Checklist for Coliform ContaminationTroubleshooting Checklist for Coliform Contamination

 

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