You should get your water tested at least once a year, or more often if you have concerns about your water's safety. If you have a private well, you are responsible for testing your own water. You can collect a sample and send it to a certified laboratory for testing or purchase a home water testing kit.
If you get your water from a public water system, the system is required to test the water regularly and provide you with a copy of the results. Contact your water utility to request a copy of the water quality report.