Be aware that if they perform the EWP near the MK, they often do so without the music.
The music can cause too much "commotion" for guests exiting the MK, so they just show the lights of the "show."
And, the "show" is not much without the music.
(Heck, it's barely anything WITH the music!

)
So, if you want to really see it, you need to go to one of the MK area resorts' beaches/boat docks.
You can see the Electrical Water Pageant from the beaches or Marinas on the open lake side of any of the MK area resorts.
Its just a very short (5-7 minutes) "show" that takes place ON the lagoon.
http://allearsnet.com/tp/ewp.htm
Although Electrical Water Pageant generally follows the schedule below... Inclement weather can cause cancellation of the pageant.
Polynesian Resort -- 9 p.m.
Grand Floridian -- 9:15 p.m.
Wilderness Lodge -- 9:35 p.m.
Fort Wilderness -- 9:45 p.m.
Contemporary Resort -- 10:05 p.m.
Magic Kingdom -- 10:20 p.m. (only during extended MK park hours)
Note that when the Magic Kingdom Fireworks are scheduled for 9 p.m., the Electrical Water Pageant runs about 7-20 minutes later.