The paragraph below is from the Florida Attorney General's website concerning free water tests:
Avoid "Free" home water tests -
Fraudulent sellers that advertise "free home water testing"
may only be interested in selling you their water treatment device, whether
you need it, or not. In performing the test, the salesperson may add tablets
or droplets of chemicals to your tap water, explaining that the water will
change color or that particles will form if the water is contaminated.
When the water changes color before your eyes, the salesperson may warn
you that the water is polluted and may cause cancer. In almost all of these
cases, any water (even spring water) would "fail" the company's
test.