For private well owners, basic testing for bacteria and nitrates is recommended by public health authorities, like the EPA or Health Canada, at least once a year. Other contaminants you may only need to test for once, such as hardness or iron, or infrequently, like radon.
![Water Testing Basics](https://blog.trojantechnologies.com/wp-content/uploads/2019/08/shutterstock_138204362-1080x675.jpg)