The new meters use wireless radio frequencies or RF, similar to wireless Internet and cable TV, which many people already have in their homes. Radio frequencies are also used in cell phones, microwaves and even baby monitors. Digital water and electric meters operate at much lower levels of radio frequencies than any of those. The meters and communication system are regulated to meet all federal communications, safety standards and codes. This is very helpful website from the Federal Communications Commission or FCC explaining radio frequencies.
You can also check the findings of the American Cancer Society.