Water landing

In aviation, a water landing is, in the broadest sense, an aircraft landing on a body of water. Some aircraft such as floatplanes land on water as a matter of course.
The phrase "water landing" is also used as a euphemism for crash-landing into water an aircraft not designed for the purpose, an event formally termed ditching. In this case, the flight crew knowingly make a controlled emergency landing on water. Ditching of commercial aircraft is a rare occurrence.
Aircraft water landings.
By design.
Seaplanes, flying boats, and amphibious aircraft are designed to take off and alight on water. Alighting can be supported by a hull-shaped fuselage and/or pontoons. The availability of a long effective runway was historically important on lifting size restrictions on aircraft, and their freedom from constructed strips remains useful for transportation to lakes and other remote areas. The ability to loiter on water is also important for marine rescue operations and fire fighting. One disadvantage of water alighting is that it is dangerous in the presence of waves. Furthermore, the necessary equipment compromises the craft's aerodynamic efficiency and speed.
Early manned spacecraft launched by the United States were designed to alight on water by the splashdown method. The craft would parachute into the water, which acted as a cushion to bring the craft to a stop; the impacts were violent but survivable. Alighting over water rather than land made braking rockets unnecessary, but its disadvantages included difficult retrieval and the danger of drowning. The NASA Space Shuttle design was intended to land on a runway instead. Some future spacecraft are planning to permit water alightings (SpaceX Dragon, Boeing CST-100, etc.)
In distress.
While ditching is extremely uncommon in commercial passenger travel, small aircraft tend to ditch slightly more often because they usually have only one engine and their systems have fewer redundancies. According to the National Transportation Safety Board, there are about a dozen ditchings per year.
General aviation.
General aviation includes all fields of aviation outside of military or scheduled (commercial) flights. This classification includes small aircraft, e.g., training aircraft, airships, gliders, helicopters, and corporate aircraft, including business jets and other for-hire operations. General aviation has the highest accident and incident rate in aviation, with 16 deaths per million flight hours, compared to 0.74 deaths per million flight hours for commercial flights (North America and Europe).
Commercial aircraft.
The FAA does not require commercial pilots to train to ditch but airline cabin personnel must train on the evacuation process. In addition, the FAA implemented rules under which circumstances (kind of operator, number of passengers, weight, route) an aircraft has to carry emergency equipment including floating devices such as life jackets and life rafts.
Some aircraft are designed with the possibility of a water landing in mind. Airbus aircraft, for example, feature a "ditching button" which, if pressed, closes valves and openings underneath the aircraft, including the outflow valve, the air inlet for the emergency RAT, the avionics inlet, the extract valve, and the flow control valve. It is meant to slow flooding in a water landing.
Aircraft landing on water for other reasons.
Aircraft also sometimes end up in water by running off the ends of runways, landing in water short of the end of a runway, or even being forcibly flown into the water during suicidal/homicidal events. Twice at LaGuardia Airport, aircraft have rolled into the East River.
"Water bird" emergency helicopter landing technique.
The "water bird" emergency landing is a technique developed by the Canadian Forces to safely land the Sikorsky CH-124 Sea King helicopter if one engine fails while flying over water. The emergency landing technique allows the boat-hull equipped aircraft to land on the water in a controlled fashion.
Launch vehicle water landings.
Beginning in 2013 and continuing into 2014 and 2015, a series of ocean water landing tests were undertaken by SpaceX as a prelude to bringing booster rockets back to the launch pad in an effort to reuse launch vehicle booster stages. Seven test flights with controlled-descents have been conducted by April 2015.
Prior to 2013, successful water landings of launch vehicles were not attempted, while periodic water landings of space capsules have been accomplished since 1961. The vast majority of space launch vehicles take off vertically and are destroyed on falling back to earth. Exceptions include suborbital vertical-landing vehicles (e.g., Masten Xoie or the Armadillo Aerospace' Lunar Lander Challenge vehicle), and the spaceplanes that use the "vertical takeoff, horizontal landing" (VTHL) approach (e.g., the Space Shuttle, or the USAF X-37) which have landing gear to enable runway landings. Each vertical-takeoff spaceflight system to date has relied on expendable boosters to begin each ascent to orbital velocity. This is beginning to change.
Recent advances in private space transport, where new competition to governmental space initiatives has emerged, have included the explicit design of recoverable rocket technologies into orbital booster rockets. SpaceX has initiated and funded a multimillion-dollar program to pursue this objective, known as the reusable launch system development program.
The orbital-flight version of the SpaceX design was first successful at accomplishing a water landing (zero velocity and zero altitude) in April 2014 on a Falcon 9 rocket and was the first successful controlled ocean soft touchdown of a liquid-rocket-engine orbital booster.
Seven test flights with controlled-descent test over-water landings, including two with failed attempts to land on a floating landing platform, have been conducted by April 2015.