I've been looking for a watch for outdoor activities, including swimming in pool and sea; no diving, though.  On the face of it, 50 meter seems pretty deep but what I found searching was that it's barely enough for hand washing.  Depending on who's talking 100 meter is enough, while other say 200 meter for my need.

What say Arfcom Jacque Cousteau?

100m+ seems fine for your use.  Screw-down crown would be best, I think.  I dive with 200M-1000M watches, but will never go deeper than 40m.  I think the ratings are based on static/non-movement, and in reality, the watch will experience stress deeper than you will be, so if you swim to 50', and knock the watch around, it'll be an effective 100m or something like that.

Casio G-shocks are great, if you like that style.

The keys are to have a modern hard type crystal, a screw back with gasket, and a screw-down crown.

Older/cheap watches use a softer plastic crystal that's installed by using a watchmakers crystal tool to compress the plastic crystal and inserting it into a step on the case.
These are not water resistant to much of any moisture.

Many cheap watches have a snap on back that may or may not have a gasket.  Again these are not moisture resistant.

A standard watch, even expensive don't have a screw down crown and the crown is a major entry for moisture.

A watch lacking the hard crystal, screw down case back, and screw down crown are not resistant to humid air, much less actual water.

A watch rated to 100 meters will serve your need AS LONG as all three of the above are in good shape.
The caskets used can deteriorate if a solvent gets on the watch, or you take a hot shower with it on.  Heat degrades the neoprene gaskets.

I almost cried when a customer brought in his brothers Sea Wolf orange dial higher end that his brother had loaned him for a Florida dive trip.
He had the watch on when he stuck his hand into a solvent of some sort, possibly gasoline.
The gaskets literally melted to a paste and the watch flooded.
It was totally rusted out by sea water so there was nothing to repair.

I suspect his brother had some comments.

Just buy a 100 meter or better watch and have it serviced every now and then to replace the gaskets and you're good for surface water sports.

Thanks, gents.  This has been very informative.

I am thinking of getting Luminox Dress Field, rated to 200m.

There are two systems of rating water resistance. The first is set up by the marketing arm of the manufacturer to target a market niche, it's rated in meters with a WR. No tests are required.

Depending on the maker if its WR200 then it would actually be designed to survive that depth but due to the variances in manufacture it may or may not actually survive. Some may not do 50m - they are betting on their customer base to accept the looks while never attempting the act. As pointed out, many who do dive rarely go more than 40m - that's 120 feet.

The second system is governed by a standard which does require the case to be tested, most do it using air pressure and calculating any changes inside to detect leaking. It gets the word "Dive" on the face with the depth in Meters. It was originally pretty good to get 100M, then the race for oneupmanship started and it's well past 200M and some models are pushing extreme depths that would actually kill the diver. But, not the watch.

The features which can survive a typical depth of 200M, strangely enough, do not require glass, screw down stems, or even a screw back case. Mineral glass is preferred for its stiffness to that depth, with sapphire glass as a upgrade. Stems are largely sealed by internal o-rings and aren't screw down in some models, if anything the screw down stem is considered a value engineered way to seal. The case back may not open at all - monocoque cases exist which have all the works inserted thru the front with the crystal fastened down and bezel placed over it. Avoiding the screwback generally raised the watch into the 300M class by avoiding the need for that gasket and periodic servicing for it.

In either case - pun intended - the works inserted has to be protected from pressure depressing either the crystal or caseback against it. Shock resistance is also rated - by it's own standard - and then dust, vibration, and temperature, too. The Casio G Shock line in both analog and digital offer a lot for the money, albeit in a quartz drive. Traditional watches tend to automatic mechanical movements, and there is some considerable difference in their inherent accuracy. Keep in mind that the inventor of quartz did so to time Olympic events that required better than mechanical measurements - athletes were actually pushing the frontiers of timekeeping. The answer was to use a vibrating quartz crystal then reduce the frequency and use the result, which then became the new standard for timekeeping.

That inventing company then saw foreign competitors use it to almost destroy their business. It was an old and open tech method with no patent or copyright. Now you know about how Rolex and the Swiss lost the technical edge and Seiko/Citizen/Casio became the world's biggest suppliers of watches.

For the most part, if a classic water resistant watch is desired, there are hundreds to choose from. If it's a Dive watch, then they are always marked Dive with meter ratings, not WR. However, the crossover of styles means its highly possible to find an attractive dive style watch with WR, or, a very upscale world timer or complication watch with Dive Rated Depth.

In my experience - fashion watches ie brands who make styles that change with the times - tend to have less robust or environmentally resistant cases. Bluntly, you buy them for their looks and if they crap out, you toss them. This seems to taper off when watch prices move past $150. Above that makers tend toward more classic styles and offer more tested Dive models as they know people are less likely to buy them frequently or in quantity.

How a watch is held onto the wrist also comes into play, some models come with integrated bracelets which are part of the artistic effort, the field, military, and dive styles tend to have interchangeable bands, straps, and/or bracelets to suit the owners needs.

Because of all that - knowing what the owner intends to do, where, and how he needs to measure time, is needed up front, and then, what appearance he/she prefers to convey as a message of who they are - or pretend to be.

Good luck with that.

Up until the later 1950's there were a lot of "Water proof" watches sold.
Then the government cracked down and they became "Water resistant" watches.

One case was a woman who bought her son a Bulova Caravelle watch and he ruined it washing his hands, this even though it was "water resistant" to 30 feet.
She demanded that the next time the Bulova salesman came through she wanted to talk to him about the guarantee

Next time he came we called her and they had a talk.
Bottom line was the Bulova man explained that when the watch left the factory it was water resistant but once it was out the door the buyer was on his own because it wasn't guaranteed to be water resistant to any depth at all.
Needless to say she was not a Bulova customer again even thought we explained that was how it was with all watch brands.

One watch that was pretty durable was the Wyler brand.  We sold a lot of these because of the Wyler reputation as a mechanic's or other occupation hard duty watch.
The cases had no back, everything went in through the front, and the balance staff was guaranteed against breakage.  They supplied us with new balance assemblies so if one was damaged we could replace it.

One reason we sold the hell out of them was that every year at the county fair the boss would have a plane fly over the fairgrounds and drop a Wyler, which was then given away in a raffle.
It had a ribbon attached so the crowd could see it fall and it would hit and bounce.
Of course the ribbon slowed the force so I suspect most watches would have made it.
The boss said they always survived the drop, but he always had another in his pocket so he could do a fast switch it if it failed.
The farmers, mechanics, and tradesmen bought a lot of Wyler's from us until they went out of business.

The late 70's were an interesting time for watchmakers.
The Bulova Accutron was an earth shaker.
The idea of a wrist watch being accurate to 60 seconds A MONTH was just astounding.

Then the first quartz LCD watches hit.
The first ones were in the $3,000 range, but within 1 1/2 years you could buy one at Walmart for $9.95.
I saw where this was going when people figured out they were like flashlights... the more you turned the display on to show all your friends, the faster the two batteries got used up.
When they figured out that the watch was $9.95 and two new batteries and the $1.00 to install them cost more then the watch, I understood that the truly disposable watch was here.
Even the old Timex wasn't totally disposable, and I replaced a lot of Timex movements.

I dove for years w/ a cheap 100m Casio attached to my BCD, and it never so much as fogged up. Deepest was 140' or so, but tons of dives 60-90'. I dove so much one summer that my wet suit never completely dried out.