I was going to post this. As I recall it is one of the hardest things I’ve ever done - and since then I’ve run marathons, boxed 10 3-minute rounds, …
Well it’s way harder than the other choice. It only takes 5 seconds to drown.
floating != treading water, as has been discussed here.
I can float for an hour. I’ve done it, no problem.
I could MAYBE tread water for an hour, if I was allowed to cheat like the OP, and take little rest breaks every 2 minutes.
If my passing a class was dependant on treading water for an hour straight, no breaks, I fail.
We had a lot of water survival in Naval flight school. IIRC, the 10-minute drill was a part of it, making you wear helmet, flight suit, survival vest, and steel-tipped boots. Then you had to do the dead-man float for many minutes, which I found hard since by that point my heart was racing.
Aside from that, we have the helo dunkers, tower jump/underwater swim, mile swim, stroke certification, parachute water ops, swim under the burning oil-slicked water, make a floatation device out of your flight suit while in the water, and some other stuff I’m forgetting. Water survival was (and still is, since every so often I have to re-qualify) one of my most physically difficult things to do in the Navy.
It is if my brother’s around. When we were kids taking swimming lessons, he would get bored treading water, so he would start spinning around and making stupid faces to make me laugh. Once I got to laughing, I’d sink like a rock, and several times thought I’d drown before I got to the edge of the pool. Bastard. 
I’m both a sinker (tons of muscle tissue) and a great swimmer, and it took me 3 tries to pass the lifeguarding test in high school because you had to tread water with only your legs for 10 minutes while holding 5 pound bricks in each hand above the water. I still say that test was No Fair.
If I got to use arms and legs (and wasn’t weighted down by heavy clothes) an hour would be no problem.
If I could do that drownproofing thing, I could go for an hour, I think. But there is no way I could pass the lifeguarding test that mlerose mentions.
Anyone else flashing on that scene in Have Spacesuit, Will Travel by Robert Heinlein where the hero tries to escape from the pit imprisoning him by blocking the water output and waiting for the thing to flood? He says “there’s no limit to the amount of time someone can stay afloat if he doesn’t panic”. And Heinlein was in the Navy, so I expect he passed a swimming test or two in his day.
Regards,
Shodan
Me too. Only I got it on the first try, but I swear it was one of the physically hardest things I’ve ever done. And that wasn’t even in clothing - it was in a swimsuit. I tried it again a couple of years later in clothes (full work clothes consisting of jeans, boots, two shirts and assorted undergarments) as part of my USFS training and damn near drowned even though I was a lifeguard and swam like a fish. After the third time I damn near drowned trying to do it, they just gave up and accepted my lifeguard certificate as sufficient to qualify me. Instead I had to swim continuously for 10 minutes in full clothes. That I could manage. I was in great shape back then, too (varity basketball and volleyball teams and I was swimming a mile a day every day). My problem wasn’t lack of fitness, it was specific gravity. I’m just not a floater. I don’t quite sink all the way to the bottom, but my natural equivalency point (the point at which I stop sinking) is about five feet down in fresh water and about two feet down in salt. Thick heavy bones and a whole, whole lot of muscle on me.
Treading water in clothing is substantially more difficult than treading water without clothing (or in a swimsuit, for example, which has generally been designed to give minimal added work to swimming). Not only does the clothing weigh more wet, it adds drag. The human body is typically near enough to neutral buoyancy that the added couple of pounds of dead weight (read: weight that adds nothing to your own buoyancy) makes a surprisingly large difference. Also, clothing adds a pretty substantial amount of drag to the motions of treading water. Fighting that drag will tire you out many, many times more quickly than treading water without the drag. This is why primary advice for “things to do if you find yourself unexpectedly in deep water” is headed up with the advice to shuck your clothes as quickly as possible. This is true even in cold water such as the north Pacific - if the clothing in question isn’t either a floatation device in disguise or a wetsuit, you’re far better off without it.
Damn. I thought my college swimming test was hard: four lengths of the pool and 15 minutes treading water; no floating allowed. And we were just wearing swim trunks. I was so tired at the end, it took me almost 5 full minutes to climb out of the pool. (The PE instructor took pity and offered to pull me out without counting it against me, but I refused out of stubborn pride.) But those lifeguard and Navy tests…wow! What’s the fatality rate on those?
[QUOTE=Shodan]
If I could do that drownproofing thing, I could go for an hour, I think. But there is no way I could pass the lifeguarding test that mlerose mentions.
Anyone else flashing on that scene in Have Spacesuit, Will Travel by Robert Heinlein where the hero tries to escape from the pit imprisoning him by blocking the water output and waiting for the thing to flood? He says “there’s no limit to the amount of time someone can stay afloat if he doesn’t panic”. And Heinlein was in the Navy, so I expect he passed a swimming test or two in his day. /QUOTE]
This is actually pretty true, provided the water isn’t too cold. Cold water changes the equation quite a bit. I’m a bona fide sinker myself, and I can keep myself from drowning for at least five hours without starting to feel tired (five hours being the longest I’ve actually attempted). However, “keeping yourself afloat” is not the same as “treading water”. Just keeping yourself afloat doesn’t take much energy even for sinkers - you have to lay back, get pretty close to horizontal in the water (actually about a 5 - 10% downward angle is pretty good for this) and keep sculling your arms and legs to maintain your face above water. That’s a materially different thing than staying upright with your whole head out water.
It’s sort of like the difference between walking and jogging. Most people in good health can pretty much walk indefinitely at a fairly slow pace (i.e., not speedwalking). People who can jog indefinitely are a much smaller subset of the population 
Staying afloat = walking, treading water = jogging, swimming = running. More or less.
Almost zero 
After all, you’re doing them in the company of a whole bunch of prospective lifeguards.
The failure rate on the first try is pretty high though. It’s not the sort of test where you have to do it on the first go, though. It’s more the sort of test where your instructor has a checklist and when he or she can check off everything on the list, you pass! A lot of people never pass, though.
For me, treading water is the easiest thing in the world and I could easily do it for an hour without any breaks. It’s quite relaxing and takes less energy than standing. I can also swim 80 to 100 feet underwater, without a diving head start. I guess I’m a bit of a fish. But ask me to dance… Wow, I’d make Elaine Bennis look like Fred Astaire. So, you know…
It’s funny, I’m always perplexed when people say, " I sink like a stone. I’d die". I mean, I know some of us are skinny, some of us are fat, some of us are tall, etc… but don’t we all inherently float? I guess not.
At our pool we have adult swim the last 15 minutes of each hour. The women head to the deep end to tread water. It’s very tiring. I can do 15 minutes. I could only do an hour if my life depended on it.
And while we’re here, can we acknowledge how difficult water polo must be? While watching the Olympic water polo matches, I kept saying out loud, “Those guys have to be in incredible shape.” I wouldn’t last 5 minutes in water polo. After the first sprint, I’d be history.