Each type of water system has many potential sources of contamination associated with it including:

• Ground water infiltration
• Surface water infiltration
• Open (improperly sealed) well casing
• No sanitary seal installed when well was originally drilled
• Cross connections are present in water system
• Unsealed water storage tanks. Water tanks are accessible to insects and small animals
• Broken water mains
• Use of pesticides, herbicides, and fertilizers within the protective 100 foot radius

Whenever potable water comes into contact with surface water, animals, animal feces, insects, or any other sort of contaminant, there is potential that the water will not be fit for human consumption. When water is tested for potability, it is tested for coliform organisms or nitrates. Before the well was put into operation, it was chlorinated to remove all coliform organisms, which may have been introduced during the drilling process. A sample was then taken to verify potability of the water.

You should not have to disinfect the well (groundwater) unless contamination has been introduced into the well subsequent to the original disinfection. However, unless you know the location of contamination, you can spend days of fruitless sampling, attempting to get a good sample. Sampling can be expensive.

Coliform samples must be taken annually to stay current with public water system sampling requirements. This sample will indicate whether any contamination is present at the time the sample was taken. You should know that contamination can occur at any time, and one sample may not indicate the true picture.

Samples should be taken from the point furthest from the water source. However, since contamination can take place anywhere, samples should be rotated throughout the system. It is good practice to have several sampling taps located at the well house in the following locations:

• Between the wellhead and any other portion of the water system.
• After any water storage tank.
• After any water treatment device.