My sister and brother-law's home in Florida has a ground water heat pump. It pulls ground water from a well on their property over the equivalent of the outdoor coil in the indoor unit, which unfortunately also houses the compressor so it is noisy, but near the garage, and a hose carries the water back out to the back yard where the water sinks into the sandy soil so fast that there is not even a wet place in the lawn. It is not very high quality water so it can't be used to add warm water to the pool, although I guess a heat exchanger could be rigged up with the pool's circulation system, but heat is not needed for the pool except for a couple of months in the spring and fall so it would probably not be worth the effort and cost. The system is economical to operate.
A friend had a big heat pump pool heater installed in his house further down the east coast of Florida and even with all of his money, he only used it for one month and did not switch it on again. Solar probably would have been a cheaper way to go but probably would not have been allowed by the homeowners' assoliation.