Count the rests - Don't count the rests?

For me, a swim workout starts when I get in the water and ends when I get out - total time.  As someone else mentioned, avg pace in a swim workout is pretty much irrelevant (IMO).  Keep track of the swim times within the set as that's what matters.  So if your workout is 10 x 100 on 1:45 (or whatever) then record what the swim times were for those 10 100s.  

x2

This is how I handle my swim workouts too.  All my other workouts as well.  I track total time and then note the intervals.

It's neither time or distance in isolation, but the composition of the workout. Say warm-up and cool-down take a total of 20 minutes combined, then you have 20 x 100, leaving say every 2:00 and note when you finish. Say 1:42-1:45 for most all of them for example. Don't fool around with getting the actual time swimming or subtracting out the rest from the main set. This is the information you want from it as there is a relationship between the work and rest you want to keep in there.

I think this is what axteraa was saying as well.

for running and cycling my "rest" between intervals is active so i'm not stopped at any point; timer is running.  when i swim i don't use a watch and just go off the pace clock at the pool.  while i might swim an average pace of 1:20-1:40 depending on the workout, i log the full hour or more in my training log as time spent in the pool.  sure it throws off the average pace, but i know and can record if i did or didn't make a certain interval in the workout that day.

I usually just go off the pace clock.  I seldom wear my watch to the pool unless I'm doing a long TT when I want to record accurate splits and total time.  I've got a waterproof notebook poolside that I use to record times, spl, etc. if I'm working on something specific.

Mark

Yes.  Don't overthink it.

No matter the discipline you're training, strap on the watch, hit start at the beginning, then just hit the lap button every time you start or stop an interval.  At the end, hit the Stop button.  For swimming, it's easiest to us the pool's clock for send-off intervals, and don't even look at your Garmin.  It's just a data collection tool.

Wear the watch or don't, that's not a big deal in itself. The more important point being made was that the thought process in the OP wasn't in quite the right direction.

I use my poolside notebook to log specific data when I'm doing stroke drills and want to log not just on interval times, but also tempo, strokes per length, etc.  Stuff that I want to analyze later.   It also helps me keep track of new workouts from my coach.

If I'm just swimming sets, I go off the pace clock.  I'm pretty good at swimming at my target paces, so will just record an average pace for a set later.

Mark

It all depends.  What's more important is how do you interpret the information you've logged.  This is where writing more than simply elapsed time and elapsed distance becomes important.  

For swims, I log the total distance and elapsed time from the wall clock.  I usually log the workout details which provide context to these two numbers.  My rest intervals are usually short so including that time doesn't have a dramatic impact on overall pace.  

Example: 2000 yards, 0:40:00
400 wu
300 kick
10x100 on 1:50, 1:33--1:37 splits
300 cd, mixed.  

Is my pace 2:00/100?  Arguably, yes.  That's what the total time divided by the total distance works out to be.  

Is my pace 1:50/100?  It can be argued this is correct as that's what the bulk of my workout was.  

Is my pace 1:35/100?  It can also be argued this is my pace.  

If I were doing a race with a 1000 yard swim, how would I use this information?  

I doubt I could do that swim in 15:50 (the 1:35/100 pace) as I probably can't sustain that pace continuously.  

I'd hope I could finish faster than 20:00 (2:00/100 pace) as I am slow kicking which I won't be doing during the race and won't be resting.  

I'd probably be a little faster than 18:20 (1:50/100 pace)

Now if I spend 5 minutes chatting with someone so it was really 45 minutes elapsed time, I'll probably remove that time from my logged workout.  

For biking and running, it depends on the duration.  For short runs, I'll stop and start my watch if I have to wait for traffic to cross a street.  For longer runs, notsomuch.  For riding, I'll rarely stop my watch when I stop for traffic, but I'll stop it if I take a break or have to do some repair or adjustment.