The answer is: Look up results of tests conducted by environmental agencies.
For example, the FDA tests give reliability to the results of improved health obtained by each company.
The FDA (The Food and Drug Administration) is a federal agency of the United States Department of Health and Human Services.
The FDA controls food safety, tobacco products, dietary supplements, prescription, pharmaceutical drugs, vaccines, biopharmaceuticals, blood transfusions, medical devices, electromagnetic radiation emitting devices, cosmetics and animal food.
Other claims are not reliable.