Only if the home is on a private well, and test the air first. Radon from well water reaches you mainly as gas released by showers and laundry. Few Greater Cincinnati homes are on wells; homes on utility water can skip this test.
More detail
Who is actually on a well here is a short list. The Kentucky Geological Survey estimated that in 2008 about 92 percent of Kenton County and 94 percent of Campbell County residents were served by public water, and about 80 percent in Boone County, and that where utility lines did not reach, only around one household in ten used a well, with cisterns and hauled water covering the rest. On the Ohio side, private wells, springs, cisterns, and hauled water systems are permitted and sampled by county health districts such as the Warren County Health District and Hamilton County Public Health, and they sit mostly on the rural edges of the metro. Water testing is its own procedure: EPA notes the devices and methods differ from air testing, the national protocol for collecting and measuring radon in water is ANSI/AARST MW-RN, and the sample has to reach a lab quickly because radon decays within days. The routine sample a health district takes is not a radon test; Warren County's checks for total coliform bacteria. In Ohio, testing water for radon for pay requires an ODH radon license, because state law defines a radon test to include water. If the water result is high, EPA describes two whole-house treatments: aeration, with typical reductions of 95 to 99 percent, and granular activated carbon, with 85 to 95 percent for moderate levels around 5,000 pCi/L or less, where radioactive byproducts can build up on the carbon. A faucet filter does nothing about the gas released in the shower, and private wells are not covered by the federal Safe Drinking Water Act, so the decision rests with you. Start with an air test using our radon testing options, and if you live in rural Campbell County, see radon testing in Alexandria.