I encourage all my swimmers to get one of these and bring it to the pool edge for every training session and every technique session. They can take notes and keep track of their training regardless of how much water gets splashed up on the deck by flip turns. Much better than trying to recollect things after they are dried and dressed. One hint: pencils work better than pens on these.
I use these for my swim workouts - it's a huge help to be able to make notes during a workout when I'm trying to figure something out, or to be able to go back and review past notes. Note - I use a mechanical pencil, as every pen I've tried (even the waterproof ones) smudge and make a mess. The pages stick together and smell funky if you don't dry it out once in a while, but that's a minor issue compared to the benefits.
I swim laps and occasionally go to water aerobics. But when I swim I admit that I lose count of how many laps I swim of this stroke and that stroke, etc. Having this at the pool edge helps so much. Two more people at the pool have bought one since I got mine. I found it works great with a pencil and it's better for me to erase when it's dry. This will be swim log forever