Regular water tests are a good idea, but even clean Wells can conceal potential problems.
Threats include cracks in the casing, dead critters in the water, Wells located in low lying, flood prone areas, or a recessed Well pit, common with older drilled Wells.
In the latter scenario, the Well casing usually stops below ground, in the pit; so if surface water floods the pit, it can overflow the top of the casing and carry contaminants into the Well.
To get a better idea of what your Well needs, contact a Licensed Well Contractor such as Burlington Water Tech.