I have the same problem, I plan to buy the [Garmin Swim watch][gsw], it has some good reviews: E.g. [DCrainmaker][dcr]

Through an accelerometer and clever software, it detects styles of swimming, measures laps, strokes, stroke rates, [SWOLF][1] and exercise time. The instrument is targeted for swimming in pools so there is no GPS.

Based on the site and the review, it seems like they have thought about the different scenarios that you have in the pool, for example, swimming laps, interval training and drills. 

[gsw]: http://sites.garmin.com/swim/
[dcr]: http://www.dcrainmaker.com/2012/06/garmin-swim-watch-in-depth-review.html
[1]: http://www.finisinc.com/blog/workouts/train-more-efficiently-with-swolf