If you've got a bit of time, I would recommend you build your own simple waterproof speaker for the pool party that you are planning to host in the summer.

It will be fun building it and will surely cost less doing than getting a finished product from JBL, for example.

I hosted a similar pool party for just my family last year, and I spent didn't cross $60. The waterproof speaker driver was around $20, I spent $11 to get the  Bluetooth amp board, $10 for the rechargeable battery, and just 5 dollars for the sealed plastic enclosure

We had massive fun, and even water splashes on the speaker didn't affect the enjoyment. So, if you mind saving some bucks, building this yourself is the right way to go.