I think that 14 CFR Section 91.205(b)(12) defines "overwater".
(12) If the aircraft is operated for hire over water and beyond
power-off gliding distance from shore, approved flotation gear readily
available to each occupant and, unless the aircraft is operating under
part 121 of this subchapter, at least one pyrotechnic signaling
device. As used in this section, “shore” means that area of the land
adjacent to the water which is above the high water mark and excludes
land areas which are intermittently under water.
Then 14 CFR Section 121.573 outlines the passenger briefing requirements for flights with overwater operations:
§121.573 Briefing passengers: Extended overwater operations.
addition to the oral briefing required by §121.571
certificate holder operating an airplane in extended overwater
operations shall ensure that all passengers are orally briefed by the
appropriate crewmember on the location and operation of life
preservers, liferafts, and other flotation means, including a
demonstration of the method of donning and inflating a life preserver.
(b) The certificate holder shall describe in its manual the procedure
to be followed in the briefing required by paragraph (a) of this
(c) If the airplane proceeds directly over water after takeoff, the
briefing required by paragraph (a) of this section must be done before
(d) If the airplane does not proceed directly over water after
takeoff, no part of the briefing required by paragraph (a) of this
section has to be given before takeoff, but the entire briefing must
be given before reaching the overwater part of the flight.
Lastly, the requirement for printed safety booklets is from 14 CFR 121.571(b) And to answer your last question, it needs to have only information pertinent to the flight, so if the airplane is not going to fly overwater at all, it doesn't need to have it.
(b) Each certificate holder must carry on each passenger-carrying
airplane, in convenient locations for use of each passenger, printed
cards supplementing the oral briefing. Each card must contain
information pertinent only to the type and model of airplane used for
that flight, including—
(1) Diagrams of, and methods of operating, the
(2) Other instructions necessary for use of emergency
(3) No later than June 12, 2005, for Domestic and Flag
scheduled passenger-carrying flights, the sentence, “Final assembly of
this airplane was completed in [INSERT NAME OF COUNTRY].”