EcoRenovator - woter to water heat exchanger question

Hi
I have been watching for a while.
I am thinking of making a heat exchanger.
I would like to start small and move on from there.
I would like to heat my 3 ft crawl space.
approx 600 square feet.
our house is on an aluvial fan with high water table and natural flow down hill.
I am wondering what is the lowest temp that would be reasonable for this to work.
I plan on digging a hole and placing a thermometer in the water.
I can place pipes uphill and use it as a horizontal well to provide a water source.

my theory is to direct the water from an up hill source to a storage unit with 2 inch pipe.(approx 150 ft run)

build the heat exchanger to use the storage as a source.
this way I could control sediment in the supply.

It appears to me the most importent thing is to know if the water has enough temp to work.

any info is appreciated