Bore water is often used by homeowners for filling swimming pools, watering the lawn or livestock, and for using in the home for flushing toilets. For drinking, cooking, or bathing, bore water usually needs to be treated so it's clean and sanitary. Even with a regular filtering process or chemical treatment, your bore water may get contaminated so that it's not safe for drinking or even for use on your lawn or for livestock. Note when it's good to have your bore water tested and why it may need to be done.
After a flood
As water flows during a flood, it brings with it a number of contaminants including pesticides, fertilizers, runoff from nearby production facilities, and the like. If the flood waters reach your bore, this can cause the water in the bore to get contaminated as well. These chemicals and other substances may be too strong to be cleaned by your standard filtering system, so it's good to have the water tested after a flood to note if you need additional materials or a stronger filter to get the water clean again.
If you have a septic tank, propane tank, or any buried tank nearby
Even if you know that a buried tank is in good condition and don't suspect it of leaking, you still should have your bore water tested more often when it's in proximity to any type of tank. You may not realize that a septic tank or propane tank is leaking, but the bacteria and other contaminants from these tanks can easily make their way into your bore. Note that even a small amount of bacteria or other substances from these tanks can contaminate your water, so don't assume you would be able to taste or smell such contamination. Have your bore water tested regularly when you have any type of buried tank nearby, even if it's on neighbor's property, so you know your water is always safe.
After spreading any type of fertilizer
You may not think that the fertilizer you use for your lawn, garden, or farm makes its way into your bore, but some types of fertilizers can become airborne so that residual amounts settle into the bore, and some get absorbed deep into the ground so the material then seeps into the bore's surrounding walls. After you've spread any type of fertilizer or if a neighbor has done so, be sure to check the water and continue to do this often so you know it's safe.