It is also possible for radon to enter your home through your water supply, though this poses a much lower risk than when it comes through the soil. If you have a private well, you can have it tested for radon. If the levels are high, you can have the water supply treated so that the radon is removed before it enters your home. If you are concerned about radon and your water comes from a public water supply, you should contact your supplier.
As with most home repairs, the cost of reducing radon in your home can vary widely, depending on how your home is built (whether you have a basement, crawlspace, or neither) and what kind of system you need.