what do you consider perfect weather

[Murloc]

wouldn't 75F ambient air temperature make the water like 50 degrees?

I know our pool feels freezing cold unless we've had a good multi-day heatwave, I imagine lakes and beach waters take significantly longer to warm up.

you can bathe in the mediterranean in October if it's a particularly nice day and you're in Sicily, but it's going to be balls cold if you do the same in May during a hot day, only germans do that.

I agree that if you own a pool, usually 23°C means that you're too early or too late in the season to have it comfortably warm exclusively through direct irradiation on the water.
There's no relation though.
You can have Föhn making the air very warm but it has no relation to water temps. The river is always colder than the lake too.

Anyway, 23°C if there's a breeze isn't that comfortable when you're getting out of not-that-warm water. I don't have a fat substratum though.

 

[NutBucket]

Anything over 75 is too hot. A day with a high temp under 55 is too cold.

Most of the USA is uninhabitable.

You sound like my Hawaiian friends.

 

[StinkyPinky]

Early 20's (around 70-75F), fine, with a slight breeze.