it’s not hard to warn a pool to bath water temps in the summer using the sun.
Now. try to warm water that comes in to the heating system at 30-45 degrees constantly while taking a shower. In the winter in the north east.
We have the opposite problem here in Central Texas.
We used to have a large in-ground swimming pool that we could only use in the fall and spring. In July and August, when it is over 100 degrees most days, the pool felt like a hot tub. We tried tossing several 50 pound blocks of ice in it, but the pool was too large for the ice to have any measurable effect.