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Is Your Drinking Water Safe?
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ISU Extension Publication #: Pm-1334i
Author: Dr. Tom Glanville, Dept. of Agricultural
& Biosystems Engineering
Date: March 1989
Content reviewed 5/95 by Tom Glanville
Safe drinking water is essential to good health. To help ensure safe water, operators of public water systems constantly watch for defects that could allow contaminants to enter. Water samples are analyzed frequently to ensure that federal drinking water standards for public water works are met.
Many Iowans, however, get their drinking water from private water systems. If your drinking water comes from a private water supply, it's up to you to make sure the system is properly inspected and tested for safety.
Inspection and Testing
Well Inspection: Loose or missing well caps, holes or cracks in the upper part of well casings, unusually low water pressure (less than 20 pounds per square inch with two fixture running), or stagnant water ponded near a well are just a few problems that can lead to contamination.
For assistance in identifying and repairing water system defects,
contact a public sanitarian, well driller, or plumber.
Water Testing: There are many potential water contaminations. It would be very costly, and in most cases, unnecessary, to test for all of them. Unless a specific contamination problem is suspected (for instance, a chemical spill or other nearby source of contamination), private well owners rely on tests for coliform bacteria and nitrate as general indicators of the safety of their drinking water. These contaminants are the most commonly reported causes of drinking water safety problems in private water systems throughout Iowa.
In fact of nearly 10,000 private water samples submitted annually to the University Hygienic Laboratory (The University of Iowa), nearly 40 percent have unacceptable levels of coliform bacteria and 15 to 20 percent exceed recommended standards for nitrate.
Every private well should be tested for coliform bacteria and nitrate at least once each year. If you suspect chemicals or other contaminants, consult your county sanitarian, the University Hygienic Laboratory the Iowa Department of Public Health, or the Iowa Department of Natural Resources about other tests that may be made.
When To Test
Some contaminants are likely to be present only during part of the year. If you want a good picture of the year-round safety of your drinking water, you must collect a sample when contaminants are most likely to be present.
Coliform bacteria an nitrate are most likely to be found during wet
weather, when runoff and excess soil moisture flush contaminants into defects in your well. Late spring or early summer are good times to test for bacteria and nitrate.
Pesticides used on the lawn, garden, or farm fields are most likely to be present in greatest concentrations (if at all) soon after they are applied. But again, it takes excess soil moisture to carry pesticides into the ground. So, late spring or early summer are good times to test for pesticides also if they are of concern to you.
The poorest times to test for water quality are during extremely dry weather or when the ground is frozen. A "safe" test result during the winter (or in a very dry season)) doesn't guarantee that contaminants won't be present during wet weather.
Where to Sample
The best place to collect a drinking water sample is at the tap you drink from most frequently. If you find that the water is unsafe, you will have to inspect your water system for defects, and collect additional samples at other locations to determine if the impurities are entering at the well or through defects in the plumbing system.
Collecting the Sample
Contact the laboratory for the appropriate sample container. Some tests, such as the one for coliform bacteria, require the sample to be collected in a sterile container. Other tests require special preservatives in the sample container. Most laboratories will supply appropriately prepared containers of suitable size when you tell them which tests you want.
To get accurate test results, be careful that you don't contaminate the sample while taking it. Avoid drawing samples in extremely dirty locations where bacteria-laden dust could enter the sterile sample container. Clean indoor locations are best. If you must use an outdoor sampling location, avoid drawing bacterial samples from frost-proof hydrants. The buried valve that allows them to drain and avoid freezing can also allow bacterially contaminated water to be drawn into the riser pipe leading to the hydrant.
Always take time to read the sample instruction provided by the
Laboratory. Once the sample is collected, get it to the laboratory as soon as possible. To ensure accuracy, many tests require that the sample be received at the laboratory within a certain time period.
Coliform bacteria samples, for example, must be received within 48 hours after sample collection. If you have difficulty getting your water samples to the laboratory by mail within 48 hours, check with your post office for advice on the best time to mail parcels. If that doesn't help, you may need to contact a carrier service that specializes in parcel delivery.
Choosing a Laboratory
In Iowa, laboratories that perform water analysis for public water
supplies must be certified by the Iowa Department of Natural
Resources. Certification helps ensure that public water supply
testing is accurate. You can benefit from laboratory certification,
too. Before selecting a lab, simply inquire if it is state-certified
to test public water supplies for the contaminants in which you are interested.
For further information about wells and water quality, ask at your
county Extension office for these Iowa State University publication:
*Pm-1329, "Coping with Contaminated Wells"
*Pm-840, "Good Wells for Safe Water"
*Pm-1328, "Plugging Abandoned Wells"
*Pm-1335, "Sampling Your Drinking Water"
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