A heat pump water heater never made sense to me: Because it pulls the heat from the surrounding air it makes the air in that room cooler. Which the main heat system has to re-warm up. So it's just making your main house heating system work harder, you might as well just power your heater with gas or electricity anyway.
A house heat pump pulls the heat in from outside, so is more efficient than a straight electric heater (there is almost always heat outside even when cold). Geothermal makes optimal sense as it pulls the heat from the ground around your home which is warm-ish even when it's truly cold.
But I don't see the logic in a heat pump water heater. Even if you exhaust the cold air outside it still pulls inside air through it which creates a vacuum in the house which just pulls air in from the outside (which is um... cold). So wut....
unfinished basement where my heat pump hot water tank lives needs cooling and dehumidifying anyways in the summer. lets my basement dehumidifier work less. and in the winter its still always above 50-55 F even pulling heat from the air as its mostly below grade. again unfinished basement, so i dont care about the temp as long as its about 55ish F or above. so it works out. only annoying thing is the noise, depending on house layout.