Just another bit of a nitpick. Water does conduct electricity, just very poorly.
Since no one really answered the OP, yes it is safe to swim when there is only a forcast of thunder storms. However, when you first hear thunder you should get out of the water and wait 15-30 minutes between the thunder claps. You are also safe to swim in rain.
I was under the impression that I had answered it, at 10:07pm on 6-28-03. Scroll up.
Thanks to all of you, esp. Early Out who makes me feel more confident about making a wise decision. Hate to be a 'fraidy cat, but not nearly as much as I hate getting electrocuted!
Sorry, but after reading the rest of the thread I had forgotten someone had said the same thing. I did however say that you can swim until you hear thunder so 
I wouldn’t be too sanguine about staying exposed until you actually hear thunder. It seems as if at least once every summer, someone gets hit by lightning out at Rehoboth or Ocean City, even when there were no immediate signs of a thunderstorm (like thunder). Once a thunderstorm watch goes into effect, I’d be a bit cautious about being out in the open, and if there’s a thunderstorm warning, I’d get to cover, even if I couldn’t actually hear the storm coming.
Of course, the beach, or a golf course, is quite a bit more exposed than your average suburban pool, which is more inclined to have trees and buildings nearby. Of course, once the lifeguard says, “Everybody out of the pool,” your options tend to get much more limited!
Uh oh, Early Out, you have me worried again. No lifeguard. Two-story buildings, trees about the same height.
Oh hell. I remember when the daughter of the governor of VA was killed by lightning on the beach on a perfectly clear day (where she was). Should I let this ruin my summer? Should I join a club with an indoor pool? Should I stop watching The Weather Channel?
Don’t worry, summerbreeze, your chances of being struck by lightning are no greater than your chances of being struck by… Oh, wait…
Seriously, though, how many people do you know who’ve been hit by lightning? How often do you hear about such cases on the local news? Compared to the dangers of driving a car, it’s a pretty low-probability event.
And those two-story buildings and trees are actually pretty good protection. Lightning is usually attracted to the tallest objects around. You, sitting by the pool, don’t present much of a target. Shoot, I spent a few summers sitting up in a lifeguard’s chair, and never even got a tingle!
Yeah, wait… 
I have been hit twice, once in 1959 and once in 1977.
My aircraft has been hit many times. ( really hard on the radios)
As far as swimming pools are concerned, you are much more likely to drown. Sounds to me like the OP is looking for a reason to stay inside.
Be sensible. But don’t worry yourself into the grave. The drive to the pool is the dangerous part.
If the lightning is going to come 20 miles and get you out of the other 30 folks in the pool or 300 on the beach, well, your number is just up.
YMMV
I think people react way too strongly to lightning. Maybe I’m stupid, but I never changed any swimming plans even during a storm. For reasons mentioned, it’s not especially dangerous to be in a pool - and the chances of the pool being struck at all are pretty damn low.
Hell, I used to swim in lake erie during storms on purpose - but that’s something most people would just find stupid. The danger there was the severe currents and undertows caused by the wind, rather than the lightning. I always found it pretty exciting - struggling against strong currents and trying not to get sucked out too far. I stopped that, though, when I got raked against a rocky cliff by severe waves several times and had my whole body bruised up.
Let me see, GusNSpot – “looking for a reason to stay inside” – hmmm, that would be the irrisistible pull of the laundry hamper, or maybe the wonders of daytime TV. Oh, wait, I don’t watch TV any more since I got the puppy.
I really want to use the pool. Last summer we were in the midst of a drought, would have been happy to have had a good rousing thunderstorm or ten. Spent the summer at the pool. This year’s different. The pool opened the end of May & I’ve been twice because we’ve had so many days of steady, hard, cold rain – and when it isn’t actually raining we’re hearing 40, 50, 60% chance of thunderstorms with potentially dangerous lightning.
Yes, I’m a bit shorter than a 2-story building, but could I (& my kids who come over to swim) be hurt if the chainlink fence were hit? Would we attract lighting if we were in the pool or sitting on the metal chairs? (I know about the danger of cars, but I don’t actually attract them.)
A woman was killed here summer before last when she was hit by lightning while crossing a parking lot at a mall. She was in an open spot between cars. I saw the spot later – the asphalt was burned. I have common sense; I’m looking for some guidelines about using it & wondering if my pool is a more dangerous place in thunderstorm weather than, say, my front yard.