Cold water

See that blue water? Pristine blue water? Do you want to know why it looks like that? I'll tell you. Because no one has put so much as a pinky-toe in there since we opened it a month ago. Why? Because it's a freakishly cold 62F, that's why.
This year was the first Memorial Day weekend we didn't jump in the pool since we moved here. Even though we are hardy Europeans, we need at least a week of temperatures in the 70s to get the water warm enough for us, and this year that just hasn't happened. We've had one day, or at the most two, of warm weather followed by a stream of dreary, chilly days.
A neighbor suggested we use solar balls to heat the water but I can't find any more information on them. Does anyone know if these things work? It says non-toxic, but what are they made of? Will they mangle the mechanics of my new pump? I'd really like to start swimming soon and I'd be willing to try these things if I knew they'd do no harm.