Hundreds of feet deep.. sure bud.

You still haven't answered the fact that you get a benefit of savings in hot summer, you know the four months you mentioned that it would benefit that ac. If you use resistance heating, it will be the same as a normal heater heater

So, even if the water heater used full resistance heating for 8 months, and heat pump to actually cool the home during the summer for 4 months... It is cheaper than a normal water heater.

It is cheaper. No way around that... And it pays for itself I'm 5-7 years.