As single engined airplanes become more advanced, they temp us away from realizing that even with their comfort and advanced technology, the safety of the flight is still dependent upon a few single point failures not occurring, and lots of preparedness if such a failure occurs in the most favourable circumstances.
I have landed in the water deliberately thousands of times, and it's been just fine - the plane was designed to do it. I have landed in the water once as a passenger when the landing did not go as planned, and the result was a life threatening dunking, surrounded by bits of sinking airplane, from which I'd been ejected underwater moments earlier - so I speak from some experience. I was wearing a life jacket, which I managed to partly inflate, and the water weather, and light conditions were as favourable as possible. The site of the crash was a two minute boat ride from shore, so the rescue was as prompt as imaginable. I survived - just.
I have taken the underwater egress course, I have been an ice water rescue trainer for more than 20 years (lots of immersion suit and cold water practice), I was properly equipped and prepared to have a collision with the water that day, and the airplane first contacted the water is a decent landing attitude and speed - and it was only just survivable.
If you ditch a fixed gear landplane, you're most likely going to end up upside down in the water - not good, but survivable if everything else goes well for you. If you ditch a retractable low wing, floatplane, or flying boat in fairly calm water, with skill, you might find yourself floating upright. In more than two foot waves, you'll either be upside down, or break up the plane. If you are ditching a plane whose flying characteristics have been degraded (airframe ice can do that), your chances of a survivable ditching have gone way down.
If your contact with the water is not a well controlled ditching (like landing on runway smoothly), you're going to have a very sudden stop, and likely break up the plane (my stop was 14G+, and I ripped the seatbelts out of the airplane as I was ejected). It is not possible to properly judge a flare for ditching over glassy water or at night. If power off, you only had one chance to guess it right, 'cause you cannot stretch your flare like a soft field landing. A power off glassy water landing will be destructive.
If you ditch into cold water, your useful life is terribly shortened before hypothermia incapacitates you. If you have wisely worn an immersion suit, your chances are much better - if you got out of the plane, and were not injured.
If you have not practiced exiting the plane, you'll drown as you go down with it. If it's daylight, you might see your way to an exit and operate it. If it's night, you won't succeed in feeling your way out, unless the door is right beside you, and operating it is instinctive for you. Have you ever been in a GA plane which was upside down? It is very disorienting, let alone being in the water. I have had to swim into an inverted floating Cessna 185 floatplane during recovery, I had to keep skimming back out to orient myself, 'cause nothing was where it should have been!
If you end up in the water, the chances are slim that anyone will help you at all in the first many minutes. If you were not wearing your lifejacket/immersion suit when you began your exit, you don't have it, and drowning or hypothermia death are very likely - particularly if you are injured. If you're in the water at night, no one will see you in time, unless you're floating safely in a raft or immersion suit - with a working light. If you're in water warm enough to not suffer hypothermia, some sea creature is probably eyeing you for dinner.
Extended over water flights in singles must be well prepared to mitigate the dangers. Pilot very well prepared as above, and self briefed. Passengers entirely aware of the risks and their duties in their own survival, and WEARING their life jacket. If an immersion suit is appropriate, only suitably trained persons (in underwater egress and immersion suit use) should be aboard at all. If you're contemplating a night flight over water in a single, you, and any other occupant of the plane must understand that no matter how well you'e prepared and briefed, the chances of surviving a water crash are about zero. You're carrying a life raft, great thinking! Hands up for pilots who have practiced and succeeded in getting into an inflated raft solo - it is nowhere near as easy as you imagine - you just keep ending up with an overturned raft over your head! Egress training!
I know that water is a fluid, but I assure everyone that when you hit it at 60 MPH, it behaves as a solid. Those one foot waves will damage a Cessna 100 sized floatplane if the landing is not excellent. If the waves are two feet plus, they will destroy a Cessna 100 sized floatplane (I've helped clean up the wrecks).
Pilots might approach an over water flight in a Tiger Moth with justified nervousness. They might be more relaxed in an advanced single with all the gadgets. The only possible two aspect of the advanced single which could improve safety would be it's retractable, so a more successful ditching in calm water and good visibility is possible, and its speed reduces your exposure time for a ditching. Otherwise, you'r chances are probably the same or a bit better in the Moth - it'll ditch at a slower speed, be easy to get out of, and will probably float displaying lots of highly visible yellow for longer! So, if you would not fly the flight over water in the Tiger Moth, probably don't fly it in any other single either!
Surviving the crash is only the first step, if drowning, becoming hypothermic, and not being found are also risks. If you choose the over water flight, think about what you're going to do, the risks, and your plan for each. If you're thinking to take a passenger (or magnitudes worse, several), as a pilot of honour, you must determine their solo capability for survival, equip them properly, and brief them before and during the flight. If you can't know for certain how you and they will survive a ditching, you and they will not. I did not plan to be ejected into the water during a crash, but I did plan for the risk of entering the water unexpectedly. I, and the pilot I was training wore our lifejackets, and survived. In both our cases, injury very certainly prevented our self rescue - floating waiting for help was the very most we could manage - help came quickly.