I enjoy lap swimming and I will tell you the most boring part of it is not having music. Its not like when your on a bike and listen to songs in a way that makes time speed up. However, when swimming there is an option.
Waterproof headsets will do the trick if they are rugged enough. This one by Toyogo is pretty good. No problems with it as long as you read the instructional manual. I thought it stopped working, wanted to return it and then read the manual. Just out of power.
It can hold up to 8K songs. That is pretty good. I can plug it into my lap top, download songs, and then listen to them while swimming. Its great to have some distraction and I soon find I am swimming longer and getting in better shape.
Now the only downside to this is the waterproof buds which are not the most comfortable but definitely bearable. You have to put them in fairly solid because any water that gets in will distort the sound. There are some other options for changing around the plugs but I haven't tried them.
$40 on Amazon.