if you want to see 'blue water' you really have two choices
you can go west to the Gulf or east to the ocean
from WDW to Clearwater beach is a tad over 90 miles so figure 90 minutes plus .... most of the way is interstate. Once at the beach, I like the Johns Pass area, which is a tad south.
http://www.johnspass.com/ the beach is nice around here and just off the beach is the 'village' with some touristy shopping and dining options. Take I-4 to Tampa then 275 to 60 and follow this west to Clearwater Beach. Most parking around this area will be by meter. When I go to Clearwater I usually go a bit farther to Pass A Grill and the Hurricane for lunch
http://www.thehurricane.com/ but it IS another 20 miles
The ocean is 60 miles east .... the first beach you'd encounter is Jetty Park at the mouth of Cape Canaveral.
http://www.jettypark.org/ There are some concessions at this park and a fee is charged per vehicle. You'd find yourself on 1A as you get close to the shore, follow this south and there will be some amount of parking (meters again) at most beach entry points. Many head the few miles further south to the Cocoa Beach Pier area
http://www.cocoabeachpier.com/ where you'll find in addition to the pier (with pay parking) some of the surfer crowd if the conditions are right. From WDW I take 417 past the airport to 528 - The Beachline - which dumps you on to A1 at Port Canaveral. (417 and 528 are toll roads ... cash accepted) For places to visit or eat, the Cove area in the port has several places to eat on the water, as does the Pier.
For me, I'd go ocean rather than gulf as it is closer (but I'm biased living here!)
Another option, but farther away is Sarasota with excellent beaches.