If you are pumping the water through a radiator, like an automobile radiator, with a fan blowing air past it the important thing is the air temperature. If you want to get water coming out of the radiator at 65 - 70 degrees you would need an air temperature of around 50 - 55 maybe even lower depending on the size of your radiator.
I suspect your air temperatures are higher than that most of the year.
You might be able to make the radiator idea work if you cooled the air going through the radiator with an air conditioner; you would need one with a rating greater than 25,000 btu per hour. But this would mean you save on water cost and pay for the electricity to run the air conditioner.
An open mind is a virtue...so long as all the common sense has not leaked out.