Maps of floodplains are being re-drawn and for now, flood insurance can be less expensive. Check out the FEMA site for current maps and explanations.
Why might a homeowner want flood insurance, despite feeling fairly secure in his or her home? Most homeowners insurances cover water damage from inside the home. If the storm drain on your street becomes clogged and overflows your basement, you will not be covered. Any water damage from outside needs to be taken care of by optional flood insurance. Depending on your area, coverage will run on average of $540/year. If you already live in a designated floodplain, the premiums may be a bit more.
So why buy now? Consider that over the past century, the water levels on the west coast have risen 7 inches. Pacific County in WA is losing shoreline faster than any other part of the country. Rivers, which may suddenly change course, will encroach on areas previously considered safe. Most importantly, once the new maps are in place, your personal castle, which you thought high and dry, may now show up in a flood plain.