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A Well Bacteria Test Fails: Now What?

by Gregg Harwood, ASHI Member
Reprinted from the December 1999 issue of the ASHI Reporter

With the recent deaths of two people and sickening of more than 700 from an E Coli contaminated well water supply at the Washington County Fair in upstate New York, it seems appropriate to review the following:

1) What the standard water potability (suitability for drinking) test tells us about the quality of the well water at rural properties, and

2) What should be done if a failed result is returned by the lab.

It's not surprising to note that one out of every five wells that we initially sample fail. Many of these failures are simply the result of a lack of maintenance. Every system and component in a house requires some degree of monitoring and maintenance to perform well over an extended period of time. As home inspectors, we know routine maintenance often goes undone, and systems fail as a result.

What gets noticed

We've also observed that the more obvious a malfunctioning component, the more likely it will get attention.

For example, a dripping tub faucet will be noticed and fixed long before concealed damage behind a leaking tile shower wall.

With this in mind, it's easy to understand that the six-inch hole in the ground - the well - gets very little attention. Like most systems, it has a finite life. It, along with every other component, will eventually wear out.

I often like to refer to what I call the

three rules of maintenance:

· Rule one - Everything requires maintenance.

· Rule two - The more obvious something is, the more likely it will be maintained.

· Rule three - Nothing lasts forever.

Many well bacteria tests failures are simply due to a lack of maintenance. However, per Rule three, some percentage of wells just have too many problems and should be replaced.

So, if 20 percent of wells fail the initial bacteria test, how do we advise our clients? I advocate following this simple approach:

· Step one - Investigate the source of the contamination and, if possible, make repairs.

· Step two - Clean the well and water supply system.

· Step three - Re-test.

· Step four - Monitor and maintain.


The water supply system can be broken down into three components: the interior piping, the well, and the water table itself. The source of contamination can be in any, or all, of these components.

Contamination sources in the interior plumbing include such things as dirty filters (which harbor and promote the growth of bacteria); broken underground pipes; and cross connections between the waste and potable water systems. Referring to the rules of maintenance, it's easy to realize that many sediment filters that we see haven't been changed in months, years, or ever.

Cross connections include garden hose bibs that don't have anti-siphon vacuum breaks. Short lengths of hose are commonly attached to utility tub faucets and can lie in wastewater. Water softener discharge tubing on many units connects directly to waste lines without stand pipes and air gaps.

Construction of the well

The well itself is constructed of a steel casing that passes through the soil layers and is driven into the bedrock. The purpose of the casing is to hold the well hole open and to seal the well from surface contamination. The cap on the well is the only owner-serviceable component. The cap should be inspected for cracks, looseness, or any other possible contaminate entry point, such as a separation in the electric conduit which could allow for the entry of rodents or insects.

The well head should project well above the surrounding soil to help minimize the chance of contamination. Often, homeowners try to conceal the well by piling soil or mulch around it, which can direct water under the cap.

The cap should be removed during inspection to check for foreign matter in the well, such as spider webs, mice, etc. Remember as water is pumped out of the well, air is drawn in, possibly pulling contaminates in through small openings around wires, etc.

The location of the well also can increase the likelihood of contamination, such as proximity to septic systems or house footer drains.

Other contamination sources

Below grade contamination sources include leaks around the pitless adapter (where the water pipe penetrates the casing below the frost line), cracks in the casing, or a poor seal to the bedrock. These defects will not be visible. Of course, it is always possible that the well is drawing water from a contaminated water table. Such things as surface run-off flowing into the aquifer through an abandoned well on an adjoining property can cause this condition.

Since many of the components aren't visible, it may not be feasible to identify every contamination source. Once a thorough visual inspection has been made, and any possible repairs have been performed, it's time to move on to the next step.


Chlorinating or "shocking" the system is the standard method of cleaning a well. Bear in mind that the purpose of this operation is to clean the system to a point where the water that is produced will pass a laboratory analysis. For this procedure to be successful, the entire system must be cleaned at the same time to avoid rapid recontamination. The theory is simple: dump bleach down the well to kill the bacteria. However, the actual procedure is time consuming and needs to be done in a systematic way

Prior to cleaning the system, purchase an inexpensive pool chlorine test kit This will be needed to tell when all the chlorine has been flushed out of the system before you re-test. Note: you can't rely on smell for this. Start the process by removing the well cap and pouring in one gallon of bleach. If the well head is not exposed (buried), it will need to be dug up and extended above grade for this procedure, and to make the well accessible for future routine maintenance. If the water source is a spring, lake, shallow well or a hand-dug well, skip this procedure and install a water purification system. By definition, these types of water sources are providing surface water" which will constantly contain bacteria. There is no way to clean them.

Once the bleach is in the well, it needs to be pumped through the entire system. Open each faucet until you can smell bleach. Don't forget the hot water faucets, hose bibs, etc. There's no science regarding the amount of bleach to add. If you can smell it at the fixtures, there's enough. If you can't smell bleach after running the water for about 30 minutes, add another gallon. In a small percentage of wells, the aquifer is flowing so rapidly that it's not possible to chlorinate. Any bleach that is added is immediately swept away In these systems, it's necessary to install a water purification system.

Once chlorine is detected at each fixture, attach a potable water hose to the hose bib and use it to spray down the interior of the well casing for about 30 minutes. This will disinfect the entire casing, not just the portion below the current water level. Don't forget to spray the cap.

Once the well casing is clean, put the cap back on and let the entire system set over night. You'll need to have bottled water on hand for drinking, cooking and washing. The chlorinated water can be used for flushing the toilet, but be careful. The bleach may irritate skin or damage clothing.

It's important to note that chlorinating the well will rile up the water and a lot of sediment and rust flakes will come out through the faucets. Aerators should be removed during this procedure to avoid clogging. Sediment filters should be replaced when the cleaning process is complete.

Flushing out the system

After the system has set overnight, the chlorine has to be flushed out. This can be a muti-day process.

First, the water heater should be drained and the fill valve shut off if possible. This unit can be refilled after the rest of the system has been flushed.

Next, hook up a hose and flush the chlorine from the system. The chlorinated water should be discharged to an area where it won't do any harm, e.g., away from sensitive vegetation and not into the septic system.

In practice, removing all the chlorine can take a couple of days. The best strategy is to pump the water out of the well as fast as possible.

Often the well is pumped down for a couple of hours, allowed to recover, and pumped down again until no chlorine is detected with the pool test kit. Even if the well is pumped "dry," there may still be five to 10 feet of chlorinated water left in the well below the pump level.

There should be no concern about burning out a modern submersible pump during this process. These pumps are rated for continuous duty Also, the motor remains submerged. However, the water discharge should be monitored for excessive sediment as the level is being drawn down and stopped if necessary

Keep in mind too that jet pumps may not be rated for continuous duty and should be monitored for overheating. If a pump fails during this process, refer back to Maintenance Rule Three: all systems have a finite life and will eventually fail.

Step Three- Re-test

Once the well system has been cleaned by chlorinating, the water should be re-tested. If it comes back from the lab with a seal of approval, proceed to the final step-monitor and maintain. If the test fails, the cleaning process should be repeated.

We often find that the first chlorinating is done in a casual manner. But once the well has failed a second time, a more thorough cleaning job is done with better results. Also, some of the bacteria can resist the chlorine for a period of time, and often a second cleaning eradicates this problem. If a second cleaning doesn't work, installation of a purification system is recommended.


Simply passing a single coliform test tells us nothing about the long-term quality of the water. The source for the initial contamination may very well remain. The only way to have confidence in the potability of the water supply is through an on-going testing program.

This program should include regular testing and keeping a running record of the results. There are no state-mandated testing requirements for private-use wells in New York, although the state has a lot of information available in a publication called, "Rural Water Supply"

Wells used in commercial facilities, such as restaurants, are required to be tested for coliform bacteria quarterly and for nitrates and nitrites annually

For a private well that has failed a potability test, or for a well that does not have a documented testing history I recommend testing once a week for a month to obtain some initial confidence in the water quality and then following the quarterly schedule previously discussed.

If the testing program shows that the well doesn't stay clean for a reasonable amount of time, I recommend that a water purification system be installed.

Estimated costs for a system are $900 to $2000. Alternately a new well may be an option if the aquifers are not the contamination source. Maintenance of the system includes changing filters as necessary and cleaning the well when testing dictates.


During the home sale process, the water potability test is universally viewed by the buyer, seller, and agents as just another hurdle to get over. However, access to clean, potable water is a basic human need.

When a city water department receives a single failed test report, the entire city is placed on a boil water advisory until the problem is fixed and a series of three consecutive tests come back OK."

The risk for a family living with a rural private water supply that has failed a test is at least the same as the city dweller when the public system fails. While the private homeowner does not have the resources of a city water department, it would be a service to clients if home inspectors were to educate them of their responsibilities to monitor and maintain their own water supply systems.

Editor's note: Prices and other information in the article pertain to New York. For water testing rules and regulations in your state, contact local government officials.