Reports are starting to come in from monitoring stations around the country indicating that trace levels of radioactive materials have been detected in the United States. In some states testing has revealed an increase in the presence of radiation in rainwater. This increase in radioactive material is linked to the incident at the Fukushima nuclear plant in Japan.
The most recent reports from the EPA continue to show that the increased levels of radiation detected are expected and still "far below levels of public-health concern". The EPA is stepping up monitoring across the country to keep an eye out for public safety. Right now there is very little cause for concern as the increase in radiation levels is expected to be short-lived.
If you are concerned about the radiation level in your drinking water you can try a water filter to remove it. The NSF lists water filter systems that are certified to reduce radium here. A basic carbon filter will not remove radium or radon. These contaminants require a Reverse Osmosis (RO) or Ultraviolet (UV) filter to remove them from drinking water. For more information on radium in water you can check out this page from the Palm Beach County Health Department. It is important to remember that we are all exposed to small amounts of radiation every day and that low level exposure over a short period of time is not a significant health risk.