Bury a rain water cistern in the yard. A 1650 gallon plastic tank will be about 6'x6' for around $500 from a farm store. You can plumb it for gravity flow into the basement, or for a cistern pump from Lehman's online catalog. Many cisterns are now attic mounted in new construction specs. Water storage and thermal mass, as well as an automatic fire extinguisher.

It doesn't have to be filled with rain water (you can use a hose), but soft water tastes 'fresher' after several years in a tank.